Methods and apparatus relating to very large scale FET arrays for analyte measurements. ChemFET (e.g., ISFET) arrays may be fabricated using conventional CMOS processing techniques based on improved FET pixel and array designs that increase measurement sensitivity and accuracy, and at the same time facilitate significantly small pixel sizes and dense arrays. Improved array control techniques provide for rapid data acquisition from large and dense arrays. Such arrays may be employed to detect a presence and/or concentration changes of various analyte types in a wide variety of chemical and/or biological processes. In one example, chemFET arrays facilitate DNA sequencing techniques based on monitoring changes in the concentration of inorganic pyrophosphate (PPi), hydrogen ions, and nucleotide triphosphates.

Electronic devices and components have found numerous applications in chemistry and biology (more generally, "life sciences"), especially for detection and measurement of various chemical and biological reactions and identification, detection and measurement of various compounds. One such electronic device is referred to as an ion-sensitive field effect transistor, often denoted in the relevant literature as ISFET (or pHFET). ISFETs conventionally have been explored, primarily in the academic and research community, to facilitate measurement of the hydrogen ion concentration of a solution (commonly denoted as "pH").
More specifically, an ISFET is an impedance transformation device that operates in a manner similar to that of a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), and is particularly configured to selectively measure ion activity in a solution (e.g., hydrogen ions in the solution are the "analytes"). A detailed theory of operation of an ISFET is given in "Thirty years of ISFETOLOGY: what happened in the past 30 years and what may happen in the next 30 years," P. Bergveld, Sens. Actuators, 88 (2003), pp. 1-20, which publication is hereby incorporated herein by reference (hereinafter referred to as "Bergveld").
FIG. 1 illustrates a cross-section of a p-type (p-channel) ISFET 50 fabricated using a conventional CMOS (Complimentary Metal Oxide Semiconductor) process. However, biCMOS (i.e., bipolar and CMOS) processing may also be used, such as a process that would include a PMOS FET array with bipolar structures on the periphery. Taking the CMOS example, P-type ISFET fabrication is based on a p-type silicon substrate 52, in which an n-type well 54 forming a transistor "body" is formed. Highly doped p-type (p+) regions S and D, constituting a source 56 and a drain 58 of the ISFET, are formed within the n-type well 54. A highly doped n-type (n+) region B is also formed within the n-type well to provide a conductive body (or "bulk") connection 62 to the n-type well. An oxide layer 65 is disposed above the source, drain and body connection regions, through which openings are made to provide electrical connections (via electrical conductors) to these regions; for example, metal contact 66 serves as a conductor to provide an electrical connection to the drain 58, and metal contact 68 serves as a conductor to provide a common connection to the source 56 and n-type well 54, via the highly conductive body connection 62. A polysilicon gate 64 is formed above the oxide layer at a location above a region 60 of the n-type well 54, between the source 56 and the drain 58. Because it is disposed between the polysilicon gate 64 and the transistor body (i.e., the n-type well), the oxide layer 65 often is referred to as the "gate oxide."
Like a MOSFET, the operation of an ISFET is based on the modulation of charge concentration caused by a MOS (Metal-Oxide-Semiconductor) capacitance constituted by the polysilicon gate 64, the gate oxide 65 and the region 60 of the n-type well 54 between the source and the drain. When a negative voltage is applied across the gate and source regions (VGS<0 Volts), a "p-channel" 63 is created at the interface of the region 60 and the gate oxide 65 by depleting this area of electrons. This p-channel 63 extends between the source and the drain, and electric current is conducted through the p-channel when the gate-source potential VGS is negative enough to attract holes from the source into the channel. The gate-source potential at which the channel 63 begins to conduct current is referred to as the transistor's threshold voltage VTH (the transistor conducts when VGS has an absolute value greater than the threshold voltage VTH). The source is so named because it is the source of the charge carriers (holes for a p-channel) that flow through the channel 63; similarly, the drain is where the charge carriers leave the channel 63.
In the ISFET 50 of FIG. 1, the n-type well 54 (transistor body), via the body connection 62, is forced to be biased at a same potential as the source 56 (i.e., VSB=0 Volts), as seen by the metal contact 68 connected to both the source 56 and the body connection 62. This connection prevents forward biasing of the p+ source region and the n-type well, and thereby facilitates confinement of charge carriers to the area of the region 60 in which the channel 63 may be formed. Any potential difference between the source 56 and the body/n-type well 54 (a non-zero source-to-body voltage VSB) affects the threshold voltage VTH of the ISFET according to a nonlinear relationship, and is commonly referred to as the "body effect," which in many applications is undesirable.
As also shown in FIG. 1, the polysilicon gate 64 of the ISFET 50 is coupled to multiple metal layers disposed within one or more additional oxide layers 75 disposed above the gate oxide 65 to form a "floating gate" structure 70. The floating gate structure is so named because it is electrically isolated from other conductors associated with the ISFET; namely, it is sandwiched between the gate oxide 65 and a passivation layer 72. In the ISFET 50, the passivation layer 72 constitutes an ion-sensitive membrane that gives rise to the ion-sensitivity of the device; i.e., the presence of—analytes such as ions in an "analyte solution" 74 (i.e., a solution containing analytes (including ions) of interest or being tested for the presence of analytes of interest) in contact with the passivation layer 72, particularly in a sensitive area 78 above the floating gate structure 70, alters the electrical characteristics of the ISFET so as to modulate a current flowing through the p-channel 63 between the source 56 and the drain 58. The passivation layer 72 may comprise any one of a variety of different materials to facilitate sensitivity to particular ions; for example, passivation layers comprising silicon nitride or silicon oxynitride, as well as metal oxides such as silicon, aluminum or tantalum oxides, generally provide sensitivity to hydrogen ion concentration (pH) in the analyte solution 74, whereas passivation layers comprising polyvinyl chloride containing valinomycin provide sensitivity to potassium ion concentration in the analyte solution 74. Materials suitable for passivation layers and sensitive to other ions such as sodium, silver, iron, bromine, iodine, calcium, and nitrate, for example, are known.
With respect to ion sensitivity, an electric potential difference, commonly referred to as a "surface potential," arises at the solid/liquid interface of the passivation layer 72 and the analyte solution 74 as a function of the ion concentration in the sensitive area 78 due to a chemical reaction (e.g., usually involving the dissociation of oxide surface groups by the ions in the analyte solution 74 in proximity to the sensitive area 78). This surface potential in turn affects the threshold voltage VTH of the ISFET; thus, it is the threshold voltage VTH of the ISFET that varies with changes in ion concentration in the analyte solution 74 in proximity to the sensitive area 78.
FIG. 2 illustrates an electric circuit representation of the p-channel ISFET 50 shown in FIG. 1. With reference again to FIG. 1, a reference electrode 76 (a conventional Ag/AgCl electrode) in the analyte solution 74 determines the electric potential of the bulk of the analyte solution 74 itself and is analogous to the gate terminal of a conventional MOSFET, as shown in FIG. 2. In a linear or non-saturated operating region of the ISFET, the drain current ID is given as:
                                          I            D                    =                                    β                                            (                                                      V                    GS                                    -                                      V                    TH                                    -                                                            1                      2                                                                                V                      DS                                                                      )                                                                V              DS                                      ,                            (        1        )            where VDS is the voltage between the drain and the source, and β is a transconductance parameter (in units of Amps/Volts2) given by:
                              β          =                      μ                                                                                C                ox                                                          (                                  W                  L                                )                                                    ,                            (        2        )            where μ represents the carrier mobility, Cox is the gate oxide capacitance per unit area, and the ratio W/L is the width to length ratio of the channel 63. If the reference electrode 76 provides an electrical reference or ground (VG=0 Volts), and the drain current ID and the drain-to-source voltage VDS are kept constant, variations of the source voltage VS of the ISFET directly track variations of the threshold voltage VTH, according to Eq. (1); this may be observed by rearranging Eq. (1) as:
                              V          S                =                              -                          V              TH                                -                                    (                                                                    I                    D                                                        β                                                                                V                      DS                                                                      +                                                      V                    DS                                    2                                            )                        .                                              (        3        )
Since the threshold voltage VTH of the ISFET is sensitive to ion concentration as discussed above, according to Eq. (3) the source voltage VS provides a signal that is directly related to the ion concentration in the analyte solution 74 in proximity to the sensitive area 78 of the ISFET. More specifically, the threshold voltage VTH is given by:
                                          V            TH                    =                                    V              FB                        -                                          Q                B                                            C                ox                                      +                          2                                            ϕ                F                                                    ,                            (        4        )            where VFB is the flatband voltage, QB is the depletion charge in the silicon and φF is the Fermi-potential. The flatband voltage in turn is related to material properties such as workfunctions and charge accumulation. In the case of an ISFET, with reference to FIGS. 1 and 2, the flatband voltage contains terms that reflect interfaces between 1) the reference electrode 76 (acting as the transistor gate G) and the analyte solution 74; and 2) the analyte solution 74 and the passivation layer 72 in the sensitive area 78 (which in turn mimics the interface between the polysilicon gate 64 of the floating gate structure 70 and the gate oxide 65). The flatband voltage VFB is thus given by:
                                          V            FB                    =                                    E              ref                        -                          Ψ              0                        +                          χ              sol                        -                                          Φ                Si                            q                        -                                                            Q                  ss                                +                                  Q                  ox                                                            C                ox                                                    ,                            (        5        )            where Eref is the reference electrode potential relative to vacuum, Ψ0 is the surface potential that results from chemical reactions at the analyte solution/passivation layer interface (e.g., dissociation of surface groups in the passivation layer), and χsol is the surface dipole potential of the analyte solution 74. The fourth term in Eq. (5) relates to the silicon workfunction (q is the electron charge), and the last term relates to charge densities at the silicon surface and in the gate oxide. The only term in Eq. (5) sensitive to ion concentration in the analyte solution 74 is Ψ0, as the ion concentration in the analyte solution 74 controls the chemical reactions (dissociation of surface groups) at the analyte solution/passivation layer interface. Thus, substituting Eq. (5) into Eq. (4), it may be readily observed that it is the surface potential Ψ0 that renders the threshold voltage VTH sensitive to ion concentration in the analyte solution 74.
Regarding the chemical reactions at the analyte solution/passivation layer interface, the surface of a given material employed for the passivation layer 72 may include chemical groups that may donate protons to or accept protons from the analyte solution 74, leaving at any given time negatively charged, positively charged, and neutral sites on the surface of the passivation layer 72 at the interface with the analyte solution 74. A model for this proton donation/acceptance process at the analyte solution/passivation layer interface is referred to in the relevant literature as the "Site-Dissociation Model" or the "Site-Binding Model," and the concepts underlying such a process may be applied generally to characterize surface activity of passivation layers comprising various materials (e.g., metal oxides, metal nitrides, metal oxynitrides).
Using the example of a metal oxide for purposes of illustration, the surface of any metal oxide contains hydroxyl groups that may donate a proton to or accept a proton from the analyte to leave negatively or positively charged sites, respectively, on the surface. The equilibrium reactions at these sites may be described by:AOH⇄AO−+Hs+  (6)AOH2+⇄AOH+Hs+  (7)where A denotes an exemplary metal, Hs+ represents a proton in the analyte solution 74, Eq. (6) describes proton donation by a surface group, and Eq. (7) describes proton acceptance by a surface group. It should be appreciated that the reactions given in Eqs. (6) and (7) also are present and need to be considered in the analysis of a passivation layer comprising metal nitrides, together with the equilibrium reaction:ANH3+∈ANH2+H+,  (7b)wherein Eq. (7b) describes another proton acceptance equilibrium reaction. For purposes of the present discussion however, again only the proton donation and acceptance reactions given in Eqs. (6) and (7) are initially considered to illustrate the relevant concepts.
Based on the respective forward and backward reaction rate constants for each equilibrium reaction, intrinsic dissociation constants Ka (for the reaction of Eq. (6)) and Kb (for the reaction of Eq. (7)) may be calculated that describe the equilibrium reactions. These intrinsic dissociation constants in turn may be used to determine a surface charge density σ0 (in units of Coulombs/unit area) of the passivation layer 72 according to:σ0=−qB,  (8)where the term B denotes the number of negatively charged surface groups minus the number of positively charged surface groups per unit area, which in turn depends on the total number of proton donor/acceptor sites per unit area NS on the passivation layer surface, multiplied by a factor relating to the intrinsic dissociation constants Ka and Kb of the respective proton donation and acceptance equilibrium reactions and the surface proton activity (or pHS). The effect of a small change in surface proton activity (pHS) on the surface charge density is given by:
                                                        ∂                              σ                0                                                                    ∂                p                                                                                H                S                                              =                                                    -                q                                                                            ∂                  B                                                                      ∂                    p                                                                                H                    S                                                                        =                                          -                q                                                                                β                int                                                    ,                            (        9        )            where βint is referred to as the "intrinsic buffering capacity" of the surface. It should be appreciated that since the values of NS, Ka and Kb are material dependent, the intrinsic buffering capacity βint of the surface similarly is material dependent.
The fact that ionic species in the analyte solution 74 have a finite size and cannot approach the passivation layer surface any closer than the ionic radius results in a phenomenon referred to as a "double layer capacitance" proximate to the analyte solution/passivation layer interface. In the Gouy-Chapman-Stern model for the double layer capacitance as described in Bergveld, the surface charge density σ0 is balanced by an equal but opposite charge density in the analyte solution 74 at some position from the surface of the passivation layer 72. These two parallel opposite charges form a so-called "double layer capacitance" Cdl (per unit area), and the potential difference across the capacitance Cdl is defined as the surface potential Ψ0, according to:σ0=CdlΨ0=−σdl  (10)where σdl is the charge density on the analyte solution side of the double layer capacitance. This charge density σdl in turn is a function of the concentration of all ion species or other analyte species (i.e., not just protons) in the bulk analyte solution 74; in particular, the surface charge density can be balanced not only by hydrogen ions but other ion species (e.g., Na+, K+) in the bulk analyte solution.
In the regime of relatively lower ionic strengths (e.g., <1 mole/liter), the Debye theory may be used to describe the double layer capacitance Cdl according to:
                              C          dl                =                              k                                                                                ɛ              0                                λ                                    (        11        )            where k is the dielectric constant ∈/∈0 (for relatively lower ionic strengths, the dielectric constant of water may be used), and λ is the Debye screening length (i.e., the distance over which significant charge separation can occur). The Debye length λ in turn inversely proportional to the square root of the strength of the ionic species in the analyte solution, and in water at room temperature is given by:
                    λ        =                                            0.3                                                                                nm                                      I                                .                                    (        12        )            The ionic strength I of the bulk analyte is a function of the concentration of all ionic species present, and is given by:
                              I          =                                    1              2                                                                  ∑                s                                                                                z                  s                  2                                                                  c                  s                                                                    ,                            (        13        )            where zs is the charge number of ionic species s and cs is the molar concentration of ionic species s. Accordingly, from Eqs. (10) through (13), it may be observed that the surface potential is larger for larger Debye screening lengths (i.e., smaller ionic strengths).
The relation between pH values present at the analyte solution/passivation layer interface and in the bulk solution is expressed in the relevant literature by Boltzman statistics with the surface potential Ψ0 as a parameter:
                              (                                    p                                                                                H                s                                      -                          p                                                                                H                B                                              )                =                                            q                                                                                Ψ                0                                      kT                    .                                    (        14        )            From Eqs. (9), (10) and (14), the sensitivity of the surface potential Ψ0 particularly to changes in the bulk pH of the analyte solution (i.e., "pH sensitivity") is given by:
                                                        Δ                                                                                Ψ                0                                                    Δ                                                                                p                                                                                H                                =                                    -              2.3                                                  kT              q                                    α                          ,                            (        15        )            where the parameter a is a dimensionless sensitivity factor that varies between zero and one and depends on the double layer capacitance Cdl and the intrinsic buffering capacity of the surface βint as discussed above in connection with Eq. (9). In general, passivation layer materials with a high intrinsic buffering capacity βint render the surface potential Ψ0 less sensitive to concentration in the analyte solution 74 of ionic species other than protons (e.g., a is maximized by a large βint). From Eq. (15), at a temperature T of 298 degrees Kelvin, it may be appreciated that a theoretical maximum pH sensitivity of 59.2 mV/pH may be achieved at α=1. From Eqs. (4) and (5), as noted above, changes in the ISFET threshold voltage VTH directly track changes in the surface potential Ψ0; accordingly, the pH sensitivity of an ISFET given by Eq. (15) also may be denoted and referred to herein as ΔVTH for convenience. In exemplary conventional ISFETs employing a silicon nitride or silicon oxynitride passivation layer 72 for pH-sensitivity, pH sensitivities ΔVTH (i.e., a change in threshold voltage with change in pH of the analyte solution 74) over a range of approximately 30 mV/pH to 60 mV/pH have been observed experimentally.
Another noteworthy metric in connection with ISFET pH sensitivity relates to the bulk pH of the analyte solution 74 at which there is no net surface charge density σ0 and, accordingly, a surface potential Ψ0 of zero volts. This pH is referred to as the "point of zero charge" and denoted as pHpzc. With reference again to Eqs. (8) and (9), like the intrinsic buffering capacity flint, pHpzc is a material dependent parameter. From the foregoing, it may be appreciated that the surface potential at any given bulk pHB of the analyte solution 74 may be calculated according to:
                                          Ψ            0                                          (                          p                                                                                H                B                                      )                          =                              (                                          p                                                                                H                  B                                            -                              p                                                                                H                  pzc                                                      )                                                                        Δ                                                                                Ψ                  0                                                            Δ                                                                                p                                                                                H                                      .                                              (        16        )            Table 1 below lists various metal oxides and metal nitrides and their corresponding points of zero charge (pHpzc), pH sensitivities (ΔVTH), and theoretical maximum surface potential at a pH of 9:
TABLE 1Oxide/Theoretical Ψ0MetalNitridepHpzcΔVTH (mV/pH)(mV) @ pH = 9AlAl2O39.254.5 (35° C.)−11ZrZrO25.150150TiTiO25.557.4-62.3201(32° C., pH 3-11)TaTa2O52.9, 2.862.87 (35° C.)384SiSi3N44.6, 6-756.94 (25° C.)251SiSiO22.143297MoMoO31.8-2.148-59396WWO20.3, 0.43, 0.550435
Prior research efforts to fabricate ISFETs for pH measurements based on conventional CMOS processing techniques typically have aimed to achieve high signal linearity over a pH range from 1-14. Using an exemplary threshold sensitivity of approximately 50 mV/pH, and considering Eq. (3) above, this requires a linear operating range of approximately 700 mV for the source voltage VS. As discussed above in connection with FIG. 1, the threshold voltage VTH of ISFETs (as well as MOSFETs) is affected by any voltage VSB between the source and the body (n-type well 54). More specifically, the threshold voltage VTH is a nonlinear function of a nonzero source-to-body voltage VSB. Accordingly, so as to avoid compromising linearity due to a difference between the source and body voltage potentials (i.e., to mitigate the "body effect"), as shown in FIG. 1 the source 56 and body connection 62 of the ISFET 50 often are coupled to a common potential via the metal contact 68. This body-source coupling also is shown in the electric circuit representation of the ISFET 50 shown in FIG. 2.
While the foregoing discussion relates primarily to a steady state analysis of ISFET response based on the equilibrium reactions given in Eqs. (6) and (7), the transient or dynamic response of a conventional ISFET to an essentially instantaneous change in ionic strength of the analyte solution 74 (e.g., a stepwise change in proton or other ionic species concentration) has been explored in some research efforts. One exemplary treatment of ISFET transient or dynamic response is found in "ISFET responses on a stepwise change in electrolyte concentration at constant pH," J. C. van Kerkof, J. C. T. Eijkel and P. Bergveld, Sensors and Actuators B, 18-19 (1994), pp. 56-59, which is incorporated herein by reference.
For ISFET transient response, a stepwise change in the concentration of one or more ionic species in the analyte solution in turn essentially instantaneously changes the charge density σdl on the analyte solution side of the double layer capacitance Cdl. Because the instantaneous change in charge density σdl is faster than the reaction kinetics at the surface of the passivation layer 72, the surface charge density σ0 initially remains constant, and the change in ion concentration effectively results in a sudden change in the double layer capacitance Cdl. From Eq. (10), it may be appreciated that such a sudden change in the capacitance Cdl at a constant surface charge density σ0 results in a corresponding sudden change in the surface potential Ψ0. FIG. 2A illustrates this phenomenon, in which an essentially instantaneous or stepwise increase in ion concentration in the analyte solution, as shown in the top graph, results in a corresponding change in the surface potential Ψ0, as shown in the bottom graph of FIG. 2A. After some time, as the passivation layer surface groups react to the stimulus (i.e., as the surface charge density adjusts), the system returns to some equilibrium point, as illustrated by the decay of the ISFET response "pulse" 79 shown in the bottom graph of FIG. 2A. The foregoing phenomenon is referred to in the relevant literature (and hereafter in this disclosure) as an "ion-step" response.
As indicated in the bottom graph of FIG. 2A, an amplitude ΔΨ0 of the ion-step response 79 may be characterized by:
                                          Δ                                                                                Ψ              0                                =                                                    Ψ                1                            -                              Ψ                2                                      =                                                                                σ                    0                                                        C                                          dl                      ,                      1                                                                      -                                                      σ                    0                                                        C                                          dl                      ,                      2                                                                                =                                                Ψ                  1                                                                  (                                      1                    -                                                                  C                                                  dl                          ,                          1                                                                                C                                                  dl                          ,                          2                                                                                )                                                                    ,                            (        17        )            where Ψ1 is an equilibrium surface potential at an initial ion concentration in the analyte solution, Cdl,1 is the double layer capacitance per unit area at the initial ion concentration, Ψ2 is the surface potential corresponding to the ion-step stimulus, and Cdl,2 is the double layer capacitance per unit area based on the ion-step stimulus. The time decay profile 81 associated with the response 79 is determined at least in part by the kinetics of the equilibrium reactions at the analyte solution/passivation layer interface (e.g., as given by Eqs. (6) and (7) for metal oxides, and also Eq. (7b) for metal nitrides). One instructive treatment in this regard is provided by "Modeling the short-time response of ISFET sensors," P. Woias et al., Sensors and Actuators B, 24-25 (1995) 211-217 (hereinafter referred to as "Woias"), which publication is incorporated herein by reference.
In the Woias publication, an exemplary ISFET having a silicon nitride passivation layer is considered. A system of coupled non-linear differential equations based on the equilibrium reactions given by Eqs. (6), (7), and (7a) is formulated to describe the dynamic response of the ISFET to a step (essentially instantaneous) change in pH; more specifically, these equations describe the change in concentration over time of the various surface species involved in the equilibrium reactions, based on the forward and backward rate constants for the involved proton acceptance and proton donation reactions and how changes in analyte pH affect one or more of the reaction rate constants. Exemplary solutions, some of which include multiple exponential functions and associated time constants, are provided for the concentration of each of the surface ion species as a function of time. In one example provided by Woias, it is assumed that the proton donation reaction given by Eq. (6) dominates the transient response of the silicon nitride passivation layer surface for relatively small step changes in pH, thereby facilitating a mono-exponential approximation for the time decay profile 81 of the response 79 according to:Ψ0(t)=ΔΨ0e−t/τ,  (18)where the exponential function essentially represents the change in surface charge density as a function of time. In Eq. (16), the time constant τ is both a function of the bulk pH and material parameters of the passivation layer, according to:τ=τ0×10pH/2,  (19)where τ0 denotes a theoretical minimum response time that only depends on material parameters. For silicon nitride, Woias provides exemplary values for τ0 on the order of 60 microseconds to 200 microseconds. For purposes of providing an illustrative example, using τ0=60 microseconds and a bulk pH of 9, the time constant τ given by Eq. (19) is 1.9 seconds. Exemplary values for other types of passivation materials may be found in the relevant literature and/or determined empirically.
Previous efforts to fabricate two-dimensional arrays of ISFETs based on the ISFET design of FIG. 1 have resulted in a maximum of 256 ISFET sensor elements (or "pixels") in an array (i.e., a 16 pixel by 16 pixel array). Exemplary research in ISFET array fabrication is reported in the publications "A large transistor-based sensor array chip for direct extracellular imaging," M. J. Milgrew, M. O. Riehle, and D. R. S. Cumming, Sensors and Actuators, B: Chemical, 111-112, (2005), pp. 347-353, and "The development of scalable sensor arrays using standard CMOS technology," M. J. Milgrew, P. A. Hammond, and D. R. S. Cumming, Sensors and Actuators, B: Chemical, 103, (2004), pp. 37-42, which publications are incorporated herein by reference and collectively referred to hereafter as "Milgrew et al." Other research efforts relating to the realization of ISFET arrays are reported in the publications "A very large integrated pH-ISFET sensor array chip compatible with standard CMOS processes," T. C. W. Yeow, M. R. Haskard, D. E. Mulcahy, H. I. Seo and D. H. Kwon, Sensors and Actuators B: Chemical, 44, (1997), pp. 434-440 and "Fabrication of a two-dimensional pH image sensor using a charge transfer technique," Hizawa, T., Sawada, K., Takao, H., Ishida, M., Sensors and Actuators, B: Chemical 117 (2), 2006, pp. 509-515, which publications also are incorporated herein by reference.
FIG. 3 illustrates one column 85j of a two-dimensional ISFET array according to the design of Milgrew et al. The column 85j includes sixteen (16) pixels 801 through 8016 and, as discussed further below in connection with FIG. 7, a complete two-dimensional array includes sixteen (16) such columns 85j (j=1, 2, 3, . . . 16) arranged side by side. As shown in FIG. 3, a given column 85j includes a current source ISOURCEj that is shared by all pixels of the column, and ISFET bias/readout circuitry 82j (including current sink ISINKj) that is also shared by all pixels of the column. Each ISFET pixel 801 through 8016 includes a p-channel ISFET 50 having an electrically coupled source and body (as shown in FIGS. 1 and 2), plus two switches S1 and S2 that are responsive to one of sixteen row select signals (RSEL1 through RSEL16, and their complements). As discussed below in connection with FIG. 7, a row select signal and its complement are generated simultaneously to "enable" or select a given pixel of the column 85j, and such signal pairs are generated in some sequence to successively enable different pixels of the column one at a time.
As shown in FIG. 3, the switch S2 of each pixel 80 in the design of Milgrew et al. is implemented as a conventional n-channel MOSFET that couples the current source ISOURCEj to the source of the ISFET 50 upon receipt of the corresponding row select signal. The switch S1 of each pixel 80 is implemented as a transmission gate, i.e., a CMOS pair including an n-channel MOSFET and a p-channel MOSFET, that couples the source of the ISFET 50 to the bias/readout circuitry 82j upon receipt of the corresponding row select signal and its complement. An example of the switch S11 of the pixel 801 is shown in FIG. 4, in which the p-channel MOSFET of the transmission gate is indicated as S11P and the re-channel MOSFET is indicated as S11N. In the design of Milgrew et al., a transmission gate is employed for the switch S1 of each pixel so that, for an enabled pixel, any ISFET source voltage within the power supply range VDD to VSS may be applied to the bias/readout circuitry 82j and output by the column as the signal VSj. From the foregoing, it should be appreciated that each pixel 80 in the ISFET sensor array design of Milgrew et al. includes four transistors, i.e., a p-channel ISFET, a CMOS-pair transmission gate including an re-channel MOSFET and a p-channel MOSFET for switch S1, and an n-channel MOSFET for switch S2.
As also shown in FIG. 3, the bias/readout circuitry 82j employs a source-drain follower configuration in the form of a Kelvin bridge to maintain a constant drain-source voltage VDSj and isolate the measurement of the source voltage VSj from the constant drain current ISOURCEj for the ISFET of an enabled pixel in the column 85j. To this end, the bias/readout circuitry 82j includes two operational amplifiers A1 and A2, a current sink ISINKj, and a resistor RSDj. The voltage developed across the resistor RSDj due to the current ISINKj flowing through the resistor is forced by the operational amplifiers to appear across the drain and source of the ISFET of an enabled pixel as a constant drain-source voltage VDSj. Thus, with reference again to Eq. (3), due to the constant VDSj and the constant ISOURCEj, the source voltage VSj of the ISFET of the enabled pixel provides a signal corresponding to the ISFETs threshold voltage VTH, and hence a measurement of pH in proximity to the ISFETs sensitive area (see FIG. 1). The wide dynamic range for the source voltage VSj provided by the transmission gate S1 ensures that a full range of pH values from 1-14 may be measured, and the source-body connection of each ISFET ensures sufficient linearity of the ISFETs threshold voltage over the full pH measurement range.
In the column design of Milgrew et al. shown in FIG. 3, it should be appreciated that for the Kelvin bridge configuration of the column bias/readout circuitry 82j to function properly, a p-channel ISFET 50 as shown in FIG. 1 must be employed in each pixel; more specifically, an alternative implementation based on the Kelvin bridge configuration is not possible using an n-channel ISFET. With reference again to FIG. 1, for an n-channel ISFET based on a conventional CMOS process, the n-type well 54 would not be required, and highly doped n-type regions for the drain and source would be formed directly in the p-type silicon substrate 52 (which would constitute the transistor body). For n-channel FET devices, the transistor body typically is coupled to electrical ground. Given the requirement that the source and body of an ISFET in the design of Milgrew et al. are electrically coupled together to mitigate nonlinear performance due to the body effect, this would result in the source of an n-channel ISFET also being connected to electrical ground (i.e., VS=VB=0 Volts), thereby precluding any useful output signal from an enabled pixel. Accordingly, the column design of Milgrew et al. shown in FIG. 3 requires p-channel ISFETs for proper operation.
It should also be appreciated that in the column design of Milgrew et al. shown in FIG. 3, the two n-channel MOSFETs required to implement the switches S1 and S2 in each pixel cannot be formed in the n-type well 54 shown in FIG. 1, in which the p-channel ISFET for the pixel is formed; rather, the n-channel MOSFETs are formed directly in the p-type silicon substrate 52, beyond the confines of the n-type well 54 for the ISFET. FIG. 5 is a diagram similar to FIG. 1, illustrating a wider cross-section of a portion of the p-type silicon substrate 52 corresponding to one pixel 80 of the column 85j shown in FIG. 3, in which the n-type well 54 containing the drain 58, source 56 and body connection 62 of the ISFET 50 is shown alongside a first n-channel MOSFET corresponding to the switch S2 and a second n-channel MOSFET S11N constituting one of the two transistors of the transmission gate S11 shown in FIG. 4.
Furthermore, in the design of Milgrew et al., the p-channel MOSFET required to implement the transmission gate S1 in each pixel (e.g., see S11P in FIG. 4) cannot be formed in the same n-type well in which the p-channel ISFET 50 for the pixel is formed. In particular, because the body and source of the p-channel ISFET are electrically coupled together, implementing the p-channel MOSFET S11P in the same n-well as the p-channel ISFET 50 would lead to unpredictable operation of the transmission gate, or preclude operation entirely. Accordingly, two separate n-type wells are required to implement each pixel in the design of Milgrew et al. FIG. 6 is a diagram similar to FIG. 5, showing a cross-section of another portion of the p-type silicon substrate 52 corresponding to one pixel 80, in which the n-type well 54 corresponding to the ISFET 50 is shown alongside a second n-type well 55 in which is formed the p-channel MOSFET S11P constituting one of the two transistors of the transmission gate S11 shown in FIG. 4. It should be appreciated that the drawings in FIGS. 5 and 6 are not to scale and may not exactly represent the actual layout of a particular pixel in the design of Milgrew et al.; rather these figures are conceptual in nature and are provided primarily to illustrate the requirements of multiple n-wells, and separate n-channel MOSFETs fabricated outside of the n-wells, in the design of Milgrew et al.
The array design of Milgrew et al. was implemented using a 0.35 micrometer (μm) conventional CMOS fabrication process. In this process, various design rules dictate minimum separation distances between features. For example, according to the 0.35 μm CMOS design rules, with reference to FIG. 6, a distance "a" between neighboring n-wells must be at least three (3) micrometers. A distance "a/2" also is indicated in FIG. 6 to the left of the n-well 54 and to the right of the n-well 55 to indicate the minimum distance required to separate the pixel 80 shown in FIG. 6 from neighboring pixels in other columns to the left and right, respectively. Additionally, according to typical 0.35 μm CMOS design rules, a distance "b" shown in FIG. 6 representing the width in cross-section of the n-type well 54 and a distance "c" representing the width in cross-section of the n-type well 55 are each on the order of approximately 3 μm to 4 μm (within the n-type well, an allowance of 1.2 μm is made between the edge of the n-well and each of the source and drain, and the source and drain themselves have a width on the order of 0.7 μm). Accordingly, a total distance "d" shown in FIG. 6 representing the width of the pixel 80 in cross-section is on the order of approximately 12 μm to 14 μm. In one implementation, Milgrew et al. report an array based on the column/pixel design shown in FIG. 3 comprising geometrically square pixels each having a dimension of 12.8 μm by 12.8 μm.
In sum, the ISFET pixel design of Milgrew et al. is aimed at ensuring accurate hydrogen ion concentration measurements over a pH range of 1-14. To ensure measurement linearity, the source and body of each pixel's ISFET are electrically coupled together. To ensure a full range of pH measurements, a transmission gate S1 is employed in each pixel to transmit the source voltage of an enabled pixel. Thus, each pixel of Milgrew's array requires four transistors (p-channel ISFET, p-channel MOSFET, and two n-channel MOSFETs) and two separate. n-wells (FIG. 6). Based on a 0.35 micrometer conventional CMOS fabrication process and corresponding design rules, the pixels of such an array have a minimum size appreciably greater than 10 μm, i.e., on the order of approximately 12 μm to 14 μm.
FIG. 7 illustrates a complete two-dimensional pixel array 95 according to the design of Milgrew et al., together with accompanying row and column decoder circuitry and measurement readout circuitry. The array 95 includes sixteen columns 851 through 8516 of pixels, each column having sixteen pixels as discussed above in connection with FIG. 3 (i.e., a 16 pixel by 16 pixel array). A row decoder 92 provides sixteen pairs of complementary row select signals, wherein each pair of row select signals simultaneously enables one pixel in each column 851 through 8516 to provide a set of column output signals from the array 95 based on the respective source voltages VS1 through VS16 of the enabled row of ISFETs. The row decoder 92 is implemented as a conventional four-to-sixteen decoder (i.e., a four-bit binary input ROW1-ROW4 to select one of 24 outputs). The set of column output signals VS1 through VS16 for an enabled row of the array is applied to switching logic 96, which includes sixteen transmission gates S1 through S16 (one transmission gate for each output signal). As above, each transmission gate of the switching logic 96 is implemented using a p-channel MOSFET and an n-channel MOSFET to ensure a sufficient dynamic range for each of the output signals VS1 through VS16. The column decoder 94, like the row decoder 92, is implemented as a conventional four-to-sixteen decoder and is controlled via the four-bit binary input COL1-COL4 to enable one of the transmission gates S1 through S16 of the switching logic 96 at any given time, so as to provide a single output signal VS from the switching logic 96. This output signal Vs is applied to a 10-bit analog to digital converter (ADC) 98 to provide a digital representation D1-D10 of the output signal VS corresponding to a given pixel of the array.
As noted earlier, individual ISFETs and arrays of ISFETs similar to those discussed above have been employed as sensing devices in a variety of chemical and biological applications. In particular, ISFETs have been employed as pH sensors in the monitoring of various processes involving nucleic acids such as DNA. Some examples of employing ISFETs in various life-science related applications are given in the following publications, each of which is incorporated herein by reference: Massimo Barbaro, Annalisa Bonfiglio, Luigi Raffo, Andrea Alessandrini, Paolo Facci and Imrich Barák, "Fully electronic DNA hybridization detection by a standard CMOS biochip," Sensors and Actuators B: Chemical, Volume 118, Issues 1-2, 2006, pp. 41-46; Toshinari Sakurai and Yuzuru Husimi, "Real-time monitoring of DNA polymerase reactions by a micro ISFET pH sensor," Anal. Chem., 64(17), 1992, pp 1996-1997; S. Purushothaman, C. Toumazou, J. Georgiou, "Towards fast solid state DNA sequencing," Circuits and Systems, vol. 4, 2002, pp. IV-169 to IV-172; S. Purushothaman, C. Toumazou, C. P. Ou, "Protons and single nucleotide polymorphism detection: A simple use for the Ion Sensitive Field Effect Transistor," Sensors and Actuators B: Chemical, Vol. 114, no. 2, 2006, pp. 964-968; A. L. Simonian, A. W. Flounders, J. R. Wild, "FET-Based Biosensors for The Direct Detection of Organophosphate Neurotoxins," Electroanalysis, Vol. 16, No. 22, 2004, pp. 1896-1906; C. Toumazou, S. Purushothaman, "Sensing Apparatus and Method," United States Patent Application 2004-0134798, published Jul. 15, 2004; and T. W. Koo, S. Chan, X. Su, Z. Jingwu, M. Yamakawa, V. M. Dubin, "Sensor Arrays and Nucleic Acid Sequencing Applications," United States Patent Application 2006-0199193, published Sep. 7, 2006.
In general, the development of rapid and sensitive nucleic acid sequencing methods utilizing automated DNA sequencers has significantly advanced the understanding of biology. The term "sequencing" refers to the determination of a primary structure (or primary sequence) of an unbranched biopolymer, which results in a symbolic linear depiction known as a "sequence" that succinctly summarizes much of the atomic-level structure of the sequenced molecule. "DNA sequencing" particularly refers to the process of determining the nucleotide order of a given DNA fragment. Analysis of entire genomes of viruses, bacteria, fungi, animals and plants is now possible, but such analysis generally is limited due to the cost and time required to sequence such large genomes. Moreover, present conventional sequencing methods are limited in terms of their accuracy, the length of individual templates that can be sequenced, and the rate of sequence determination.
Despite improvements in sample preparation and sequencing technologies, none of the present conventional sequencing strategies, including those to date that may involve ISFETs, has provided the cost reductions required to increase throughput to levels required for analysis of large numbers of individual human genomes. The ability to sequence many human genomes facilitates an analysis of the genetic basis underlying disease (e.g., such as cancer) and aging, for example. Some recent efforts have made significant gains in both the ability to prepare genomes for sequencing and to sequence large numbers of templates simultaneously. However, these and other efforts are still limited by the relatively large size of the reaction volumes needed to prepare templates that are detectable by these systems, as well as the need for special nucleotide analogues, and complex enzymatic or fluorescent methods to "read out" nucleotide sequence.

Methods and apparatus for measuring analytes using large scale FET arrays


An electrically conductive article such as a sheet having holes therein is coated with a dielectric polymer using a multi-stage electrophoretic deposition process. A coating of uncured polymer is deposited electrophoretically and then cured. After the first polymer is cured, the part is subject to a further electrophoretic deposition process and further curing. Use of a second electrophoretic deposition step allows effective coating of parts having small holes without plugging the holes. The coated parts may be used as microelectronic connection components such as chip carriers used in packaging semiconductor chips.

The present invention relates to fabrication of circuit components for use in microelectronics by electrophoretic deposition.
Microelectronic assemblies and sub-assemblies such as packaged semiconductor chips, multi-chip modules, and larger circuits utilize many components which include dielectric layers and conductive, typically metallic components on such dielectric layers. For example, as disclosed in commonly assigned U.S. Pat. Nos. 5,148,265; 5,489.749; and 5,518,964, the disclosures of which are hereby incorporated by reference herein, a chip package may include a generally flat, sheet-like dielectric element having metallic conductive features such as terminals, and in some cases, electrically conductive traces extending along a surface of the sheet. These traces may be formed integrally with flexible leads which serve to connect the terminals to contacts on a semiconductor chip. Typically, the sheet-like dielectric element is flexible and is positioned adjacent to the chip. For example, the sheet-like element may overly a surface over the chip and a compliant layer may be provided between the dielectric element and the chip. These elements are sometimes referred to as a xe2x80x9cchip carriersxe2x80x9d or xe2x80x9cinterposers.xe2x80x9d
Other structures used in microelectronics include single layer and multi-layer circuit panels such as those described, for example, in commonly assigned U.S. Pat. Nos. 5,570,504 and 5,558,928, the disclosures of which are hereby incorporated by reference herein. These circuit panels include one or more layers of a dielectric material with conductive traces extending along the dielectric material. Still other components used in microelectronics include sockets such as those described in commonly assigned U.S. Pat. No. 5,632,631 and commonly assigned PCT International publication WO97/44859, the disclosures of which are also incorporated by reference herein. Conductive features on microelectronic components such as packaged semiconductor chips may be engaged with these sockets to make a temporary or permanent electrical connection.
These aforesaid components most commonly are fabricated by techniques similar to those used to manufacture flexible printed circuits. Such techniques use pre-formed sheets of flexible dielectric materials, most commonly Polyimide and form metallic features on these sheets. For example, metallic features can be formed by selectively depositing metals such as copper on the dielectric sheets, or by laminating the dielectric sheets with sheets of metal and etching the metallic sheets to form the required metallic features. The metallic features in some instances include metallic features extending vertically through a sheet, between its major surfaces, commonly referred to as xe2x80x9cvias.xe2x80x9d Vias typically are formed by depositing metal into holes extending through the dielectric layer as, for example, by processes such as sputtering, electroless plating and electroplating. As described in some of the foregoing documents, microelectronic connection components such as chip carriers, circuit panels and sockets may incorporate electrically conductive potential plane elements, typically the form of thin, sheet-like metallic layers overlying a dielectric layer or sandwiched between dielectric layers. These potential plane elements typically are connected to a source of a constant potential such as power or ground potential.
As described, for example, in U.S. Pat. No. 5,590,460, the disclosure of which is incorporated by reference herein, layers for use within multi-layer circuit panels have been fabricated by providing a metallic sheet with holes extending through the sheet and depositing a polymeric material such as an epoxy or an acrylic polymer using an electrophoretic deposition process. In the electrophoretic deposition process, the sheet is immersed in a bath containing uncured polymer. An electrical potential is maintained between the sheet and a counterelectrode in contact with the bath. The electrical field causes the uncured polymer to deposit as a thin coating on the sheet. After coating, the sheet is removed from the bath and the still adhering droplets of the bath are removed, as by rinsing the sheet. The uncured polymer is then cured, typically by baking the sheet at an elevated temperature. The resulting continuous dielectric coating covers the major surfaces of the sheet and extends through the holes as well, so as to form hollow dielectric liners extending within the holes of the sheet. As also described in the ""460 patent, metallic structures can be formed within the holes of such a layer and can be used to connect adjoining layers of the multi-layer circuit with one another.
Arachtingi, U.S. Pat. No. 4,601,916 discloses a multi-step process in which insulation is provided on opposed surfaces of a metallic sheet; holes are formed in the composite assembly thereby exposing some of the metal within the holes and the metal is then etched back thereby enlarging the holes. Following this etching step, a coating is applied onto the exposed metal surfaces within the holes by an electrophoretic deposition process. Fletcher et al. U.S. Pat. No. 4,714,646 and Japanese patent publication JP01-225197 describe electrophoretic deposition processes forming circuit panel elements. Another process, taught in U.S. Pat. No. 4,783,247 utilizes electrophoretic coating after electrostatic spray coating of metallic cores having holes therein. Still other processes involving electrophoretic deposition of insulators on metal cores of circuit panels are disclosed in Thams, U.S. Pat. No. 4,321,290. Kodani et al., U.S. Pat. No. 5,738,928 discloses a tape automated bonding (xe2x80x9cTABxe2x80x9d) tape using a metal core coated with an insulating adhesive material.
Despite considerable interest in the art in using electrophoretic deposition of an insulating layer on a metal conducting layer to make metal core layers, these processes have not been adopted in fabrication of chip carriers heretofore. Certain chip carriers require very fine vias, having diameters below about 100 xcexcm (0.004 inches) and in some cases 75 xcexcm (0.003 inches) or less. Processing problems arise when attempts are made to use conventional electrophoretic deposition processes to provide polymeric linings in such small holes in conjunction with continuous polymeric coatings on the surfaces of a metal or other conductive layer. In some instances, the cured polymeric material does not form a continuous polymeric coating over all of the interior surfaces of the holes. Attempts to correct this problem by increasing the time of exposure to the polymeric coating bath or by increasing the electrical potential applied during the coating process can provide a heavier polymeric coating. However, the polymeric coatings typically still suffer from defects within the interior of the holes. If the coating weight is increased to a point where the defects disappear, the coating typically plugs the holes, making it impossible to form conductive structures within the holes.
One aspect of the present invention provides an improved process for making microelectronic components. The process according to this aspect of the invention includes the step of providing an electrically conductive, typically metallic element such as a sheet or a lead frame having oppositely facing first and second major surfaces and having holes extending through the sheet. A first coating of uncured polymer is deposited by electrophoretic deposition, preferably by immersing the conductive sheet in a liquid bath containing an uncured polymer, contacting the bath with a counterelectrode and applying an electrical potential between the counterelectrode and the conductive sheet to coat the sheet with uncured polymer. After this deposition step, the sheet is removed from the bath and preferably freed from excess polymer by rinsing or otherwise removing loosely adhering polymer and bath solution. The uncured polymer on the sheet is then cured to form a first dielectric coating, typically by heating. After the first dielectric coating is deposited, the electrophoretic deposition process is repeated using a different polymer bath or, preferably, a bath containing the same polymer as used in the first electrophoretic deposition process. The sheet is once again removed from the bath and loosely adhering solution is removed, whereupon the sheet is subjected to a second curing process to cure the coating applied in the second electrophoretic deposition step. The resulting coated sheet has a cured polymeric layer overlying the conductive sheet and forming a continuous dielectric liner within the holes. The process can provide reliable, continuous dielectric liners within holes smaller than 100 xcexcm in diameter and in some cases, smaller than 75 xcexcm without plugging the holes with the dielectric material, and can also form reliable coatings within larger holes. Although the present invention is not limited by any theory of operation, it is believed that the dielectric film formed by the first curing step provides good coverage of the major surfaces of the element, so that any uncovered areas are concentrated in the interiors of the holes. Thus, the second electrophoretic deposition step is believed to deposit the uncured polymer selectively at any exposed conductive areas of the sheet, within the holes. Moreover, the cured polymer deposited in the first stage encircles the holes at the major surfaces during the second curing step. The uncured polymer at the interior surfaces of the holes may become liquid or partially liquid during the second curing step. The cured polymer encircling the holes may assure that surface tension or shrinkage of the polymer does not cause retraction of the polymer layer from the interior surfaces of the holes during the second curing step. Regardless of the mechanism of operation, it has been found that procedures according to this aspect of the present invention can provide reliable dielectric coverings of the metallic element, including the interiors of the holes, under conditions which do not result in the filling of the holes by the dielectric material, even where the holes are very small.
Most preferably, the conductive element is a metallic sheet or other metallic part between about 10 xcexcm and 100 xcexcm thick. The holes may be formed in the metallic element by conventional processes such as selective electrochemical etching or mechanical punching. After the holes are formed, the metallic element desirably is subjected to an electropolishing process. In the electropolishing process, the metallic element is immersed in a liquid electrolyte and the metallic element is maintained at a positive electrical potential with respect to a cathode also immersed in the electrolyte, so that metal is removed from the element by electrolytic action. The electropolishing process forms smooth surfaces within the holes and the major surfaces. This facilitates reliable formation of dielectric layers.
Another aspect of the present invention includes a microelectronic structure including an electrically conductive metallic core having a pair of oppositely facing major surfaces and having holes extending therethrough smaller than 100 xcexcm and desirably smaller than 75 xcexcm in diameter. The component further includes a polymeric dielectric layer overlying and adhering to the metallic core and extending into the holes, the coating being such that it does not completely fill the holes. Most preferably, metallic conductive elements extend through the holes and are isolated from the core by the polymeric dielectric layer within the holes.
Yet another aspect of the present invention provides a chip carrier for use in making a packaged semiconductor chip. A chip carrier in accordance with this aspect of the present invention includes a structure having a sheet-like metallic core, a polymeric dielectric coating overlying and adhering to the metallic core and terminals disposed on the coating so that the coating maintains at least some of the terminals electrical isolated from the core. The chip carrier also includes flexible leads connected to the terminals and extending from the structure for bonding to contacts of a semiconductor chip. The structure may have one or more bond windows. In this case, the metallic core desirably has apertures at each such bond window and the coating extends into the apertures of the core and covers the metallic core within the bond windows. The flexible leads desirably extend at least partially across the bond windows so that the regions of the leads within the bond windows may be bonded to contacts on the chip. One or more of the flexible leads may be electrically connected to the core to serve as a ground or power leads to the chip. Chip carriers according to this aspect of the invention may also include small vias extending through holes in the core, these vias being insulated from the core by portions of the polymeric dielectric coating extending into the holes. Still further aspects of the invention include microelectronic assemblies including chip carriers as aforesaid.
These and other features and advantages of the present invention will be more readily apparent from the detailed description of the preferred embodiments set forth below, taken into conjunction with the accompanying drawings.

Forming microelectronic connection components by electrophoretic deposition


A socket comprising a body having an opening in which a contact-holder is housed, a cover articulated to the body and movable between a closed position in which it closes said opening and an open position in which it is raised from said opening, a yoke articulated to the body and movable between a lowered position and a raised position, the yoke having two arms which, in the lowered position, are intended to cooperate with a shoulder of a plug to retain the plug inserted into the socket, and a latch member articulated to the yoke and movable with respect to the yoke between a locked position and an unlocked position, the latch member having at least one pawl which, in the locked position, engages a corresponding seat of the body and which, in the unlocked position, is disengaged from said seat, and a cover-lock element articulated to the body and movable between an engaged position and a disengaged position, wherein the latch member has at least one cam portion that cooperates with the cover-lock element for moving the cover-lock element from the engaged position to the disengaged position when the latch member moves from the locked position to the unlocked position.

1. Field of the Invention
The present invention relates to a socket for a connector assembly, particularly intended for the electrical connection between a towing vehicle and a trailer, or between a tractor and an implement.
2. Description of the Related Art
The control devices used on vehicles for towing trailers or on agricultural tractors increasingly require signals that are transmitted by means of a CAN (Controller Area Network) bus between the tractor and a tool or between a towing vehicle and the trailer.
The ISO standard 11783-2 defines the characteristics of the connectors used for the electronic interconnection, e.g. between tractors and implements. The sockets for the electrical connectors, according to the ISO standard 11783-2, must be well sealed to prevent the entry of water, dust, or other contaminants, which could compromise the transmission of signals.
The document EP-A2-1492203 describes a socket according to the ISO standard 11783-2, comprising a body having an opening in which a contact-holder is inserted. The opening is closed with a cover articulated to the body. The socket comprises a yoke articulated to the body and movable between an open position and a closed position. The yoke is designed to engage a plug to hold it in an engaged position with the socket. A latch member is coupled to the yoke to lock the yoke in an engaged position.
The socket described in the document EP-A2-1492203 has the disadvantage that the cover is not locked in the closed position. Consequently, during cleaning operations of the socket to remove dirt deposits, the cover can lift up and open, allowing the infiltration of moisture into the socket and into the switching circuit. This particularly applies in the case of cleaning with high-pressure washing devices.


A living website is provided that autonomously and dynamically changes presentation based on engagement from users, business members, distributed devices, and, optionally, individual user preferences. The living website presentation changes with the promotion and demotion of website elements through repositioning, visual differentiation, and other means. These changes are produced by a machine rewriting of the living website code that is conditioned on the continually tracked engagement. In particular, the tracked engagement identifies the website elements that are most engaging at that time. The living website then adapts in order to presents users with this most engaging content in a manner that is immediately apparent and before them. Consequently, users spend less time searching, scrolling, or otherwise browsing a website in order to find content that is engaging and of interest to them, and more time interacting with the engaging content that is already before them.

Review websites can have a significant impact on a business. A sufficient number of negative reviews or ratings can persuade potential customers to go elsewhere. A sufficient number of positive reviews or ratings can persuade new customers to give the business a try or persuade customers deciding between two or more businesses to try the business with the most positive reviews or ratings.
Due to the importance that individuals place on the experiences of others, review websites have become the defacto website for many businesses. This is especially true for review websites that aggregate various information (e.g., hours of operations, contact information, addressing, menus, pricing, etc.) with the reviews and ratings of individuals. In other words, potential customers may visit the review website instead of or in addition to the business's own website, and lean more heavily on the information from the review website than the business's own website when deciding whether to visit or transact with the business.
There are however several shortcomings with these review websites. False and inaccurate information can be posted with no verification. Reviews and ratings persist and follow the business regardless of whether or not the business has changed for the better or worse. Reviews and ratings have equal effects on a business regardless of whether a review or rating focuses on an insignificant, inconsequential, or temporary aspect of the business as opposed to the primary focus or permanent fixture of the business. For instance, a first reviewer may post a negative review because the reviewer disliked the parking in nearby streets around a restaurant on a particular day, while a second reviewer may post a positive review that the food from the restaurant was exquisite. Review websites treat these two posts equally. Consequently, the two posts can have equal affect on the business unless a reader takes the time to dissent the text of each individual post. These and other issues arise with nearly every review website because the content is not curated or verified. The content is simply aggregated in one place regardless of its focus and relevance, and the business has little to not control over what others publish as factual information about the business.
Accordingly, there is a need to more effectively engage consumers and businesses, and provide a single portal whereby accurate information from both parties is presented and is curated according to the provided information. In other words, there is a need to replace the simple aggregation and sequential add-on of every review and rating approach of review websites with a dynamically generated website that continually changes based on timely, relevant, and accurate information contributions from consumers and the business, whereby the presentation of the dynamically generated website can be further customized according to individual customer preferences or offerings of the specific business. There is a further a need to spur engagement of customers and businesses and for the dynamic website generation to occur non-intrusively. To this end, there is a need to incorporate distributed devices from which objective and accurate information can be used to supplement the posts of individuals or to verify the accuracy and content of those posts.

Autonomous and dynamic generation of a living website for continuous user engagement


A heat exchanger for an air conditioner outdoor unit includes tubing of the microchannel type which is internally partitioned into separate, parallel refrigerant flow passages and a wrapping of heat conductive flexible heat transfer material, commonly known as spine fin. The heat exchanger provides for greater heat transfer and a more compact package. Further, such heat exchangers allow for a reduced refrigerant charge in the air conditioning unit in which they are used.

The present invention relates generally to heat exchangers. More particularly, the present invention relates to heat exchangers through which a refrigerant flows in heat exchange contact with ambient air flowing over an external surface thereof. With still more particularly, the present invention relates to a heat exchanger for an outdoor unit of an air conditioner or heat pump which employs tubing having multiple discrete flow paths for refrigerant therethrough and onto which so-called spine fin heat transfer surface is wrapped or otherwise bound.
The use of heat exchangers having a spine fin heat transfer surface in certain air conditioning applications is known as is the use of so-called microchannel tubing in certain other and different heat exchanger applications. Exemplary of the use of spine fin heat transfer surfaces in the outdoor heat exchanger coils of residential air conditioners is U.S. Pat. No. 4,535,838, assigned to the assignee of the present invention and incorporated herein by reference. It will be noted that in prior spine fin applications, tubing which is circular in cross-section and which defines a single internal refrigerant flow passage has been the norm.
Microchannel tubing is known to be used in automotive radiators. The design of such radiators calls for the brazing of fins, in a controlled fashion utilizing relatively expensive and energy consuming brazing furnaces, to the microchannel tubing or for the mechanical deformation of the tubing or its fins so as to rigidly ensconce the tubing in the fin surface with which it is used. The latter is illustrated by U.S. Pat. No. 3,603,384.
Heat exchangers have also been made using microchannel tubing in which heat transfer fins are formed by a process of gouging or otherwise forming the exterior surface of tubing itself so as to create fin-like projections. Illustrative in that regard is U.S. Pat. No. 3,886,639.
A need has been identified to minimize the operating refrigerant charges used in air conditioning units, heat pumps, and other such apparatus of the type used to cool and/or heat homes and small commercial establishments and to reduce or at least maintain the costs associated with the manufacture of such devices. This need arises from the increasing expense of raw materials used in the manufacture of heat exchangers for use in such applications, from increased prices for existing refrigerants, from the introduction of newer, higher pressure refrigerants and from a demand for more compact and less obtrusive outdoor units where the space in which to dispose such units may be at a premium. Existing outdoor heat exchanger coils for such applications are not sufficiently strong, economical of manufacture or efficient from a heat exchange standpoint to meet all of such demands.

Heat exchanger having microchannel tubing and spine fin heat transfer surface


A coupling structure between a cylindrically united end portion of a breeches pipe and a cylindrical end portion of a tubular pipe. The cylindrically united end portion has at diametrically opposed portions thereof respective grooves each extending axially from a circular end of the cylindrically united end portion. The cylindrical end portion of the tubular pipe has at diametrically opposed portions thereof respective slots each extending axially from a circular end of the cylindrical end portion. The cylindrically united end portion of the breeches pipe is inserted into the cylindrical end portion of the tubular pipe in such a manner that grooves are mated and merged with the slots respectively. The circular end of the tubular pipe is entirely welded to an outer surface of the cylindrically united end portion of the breeches pipe and a periphery of each slot is entirely welded to the corresponding groove to achieve a hermetic sealing therebetween.

1. Field of the Invention
The present invention relates in general to a structure for coupling pipes, and more particularly to a structure for coupling a tubular pipe with a breeches pipe, which is used in an exhaust manifold of an automotive internal combustion engine. More specifically, the present invention is concerned with a structure for coupling, via welding, a cylindrically united end portion of the breeches pipe with one cylindrical end portion of the tubular pipe.
2. Description of the Prior Art
In an exhaust system of an automotive internal combustion engine, there is provided an exhaust manifold which carries waste emissions away from the combustion chambers of the engine. Some of the exhaust manifolds are of a type which comprises a plurality of tubular pipes each of which has one end connected to an exhaust pipe of the exhaust system and corresponding number of breeches pipes each of which has a cylindrically united end portion coupled, via welding, with the other end of each tubular pipe and separated two ends respectively connected to exhaust ports of the engine.
Some structures for coupling, via welding, the united end of a breeches pipe with a tubular pipe are described in Laid-open Patent Application 57-47523, which are schematically shown in FIGS. 4, 5, 6 and 7 of the accompanying drawings.
As is shown in FIG. 4, in one conventional coupling structure, a cylindrically united end of a breeches pipe 11 is connected via welding "W" to one end of a tubular pipe 13.
FIGS. 5A, 5B and 5C show the method of producing the breeches pipe 11. As shown in FIG. 5A, for the production, a straight tubular pipe 15 is used, which has a flat portion 15a formed on a cylindrical wall thereof. Thus, the cross section of the pipe 15 at the flat portion 15a is shaped to have a straight part 15b and an arcuate part 15c, as shown. Then, as is shown in FIG. 5B, the pipe 15 is cut at only the semi-cylindrical wall 15c except the flat portion 15a, and then, as is shown in FIG. 5C, the pipe 15 is folded largely in two along the cut portion.
However, in the structure of FIG. 4, the coupling between the breeches pipe 11 and the tubular pipe 13 is somewhat weak because of inherency of such coupling structure. That is, as shown, the two members 11 and 13 are mated in a so-called end-to-end connecting manner and welding "W" is applied to only the mated end portions, which fails to allow the coupling therebetween to exhibit a satisfied unifying force.
In order to solve the above-mentioned drawback, one measure has been thought out which is shown in FIG. 6. That is, in this measure, the cylindrically united end portion 11a of a breeches pipe 11 is snugly inserted in one end of a tubular pipe 17, and welding "W" is applied to a portion where a leading end of the pipe 17 is mated with the cylindrical wall of the united end portion 11a of the breeches pipe 11.
However, even this coupling structure has a drawback which is depicted by FIG. 7. That is, as shown, due to inherency of such coupling structure, there are remained certain gaps "S" between the inserted united end portion 11a of the breeches pipe 11 and the tubular pipe 17, each axially extending along the mated edges of the folded two parts of the pipe 11. In fact, such gaps "S" originate from grooves which are inevitably produced when the straight tubular pipe 15 (see FIGS. 5A, 5B and 5C) is folded into two. Such gaps "S" however bring about a higher possibility of leakage of exhaust gas to the open air therethrough. Even though such leakage can be minimized by covering the spaces "S" with welding "W", complete suppression of leakage is not achieved because welding "W" can not be applied to the entire length "L" of the united end portion 11a of the breeches pipe 11 which is received in the tubular pipe 17.

Structure for coupling pipe with breeches pipe


The invention provides a method for regenerating viable and fertile Citrus plants by tissue culture from explants of field-grown mature trees, said method comprising the steps of incubating the explant in agarified media to develop axillary buds, subculturing the explant alongwith sprouted axillary buds in agarified media, excising the meristem domes along with leaf primordia in another medium to generate shoots, subculturing the meristem-regenerated shoots on filter paper bridge employing a liquid medium in order to obtain healthy shoots of an average length of about 1.5 cm without intervening callusing within a period of 20-25 days, proliferating the meristem-regenerated shoots in agarified media to obtain well-developed shoots, rooting the isolated well-developed shoots in agarified media, transferring the freshly developed roots of Citrus sinensis to a different medium while allowing the shoots of C. aurantifolia to grow in the same medium for about 15 days to develop tap roots, hardening the rooted shoots ex vitro in a liquid medium, and allowing the shoots to grow in the same medium under incubation conditions, transferring the hardened shoot meristem-raised plants to soilrite in pro-trays for ex vitro growth for about 7 days to ensure 95% to 100% survival of the shoot meristem raised Citrus plants.

The invention provides a method for in-vitro regeneration and proliferation of excised shoot meristems of Citrus aurantifolis (Christm.) Swingle and C. sinensis (L.) Osbeck.
In essence, the present invention discloses sequential culture conditions, including growth media for in vitro culture of excised shoot meristems taken from field-grown mature trees of Citrus aurantifolis (Christm.) Swingle and C. sinensis (L.) Osbeck (sweet orange), their regeneration into individual shoots or proliferation, rooting of the isolated meristem-regenerated shoots, hardening of such in vitro-raised plantlets and their successful ex vitro growth.
Citrus is the most important fruit of the world, second to grape in commerce and the third important fruit of India so far as production is concerned. However, considering the nutritional value for human health and the large number of products made from it, Citrus may qualify to be the number one fruit of the world.
Citrus plant is vulnerable to infection by a number of pathogens, particularly viruses, viroid, mycoplasma and BLO (bacteria-like organism) besides bacteria and fungi (Spiegel-Roy, P. and Goldschmidt, E. F. 1996. Biology of Citrus, Cambridge University Press, U.K.), which take a heavy toll of citrus fruit production. According to the latest figures available, citrus produce (oranges) in India is less than that produced in Spain in 1992-93.
Also, whilst Spain is the largest exporter of citrus fruit, India exports none (Spiegel-Roy, P. and Goldschmitt, E. F. Biology of Citrus, Cambridge University Press, U.K.), which is paradoxical in view of the far greater citrus orchard area in India as compared with Spain.
The enviable position acquired by Spain in citrus production is mainly due to tissue culture application, particularly micrografting, through which virus-free orchards have been produced, since shoot meristem in citrus is free from viruses and hence, the resulting plant from it is also free from viruses (Murashige, T., Bitters, W. P., Rangan, T. S., Nauer, E. M., Roistacher, C. N. and Holliday, P. B. 1972. A technique of shoot apex grafting and its utilization towards recovering virus-free Citrus clones. Hort Science 7: 118-119; Navarro, L., Roistacher, C. N. and Murashige, T. 1975. Improvement of shoot-tip grafting in vitro for virus-free citrus. J. Amer. Soc. Hort. Sci. 100: 471-479; Navarro, L. 1992. Citrus shoot tip grafting in vitro. In: Biotechnology in Agriculture and Forestry, Vol. 18. Ed. Y. P. S. Bajaj, pp.327-338, Springer-Verlag, Berlin).
Shoot meristem alone, i.e., consisting of apical dome or accompanied by 1, 2 or 3 youngest leaf primordia, measuring 1 mm or less than 1 mm in length comprises meristem culture. It is the best explant for cloning as well as for elimination of pathogens, as its constituent cells are genetically uniform and mostly free from pathogens. Culture of shoot meristem of Citrus is extremely significant, as it has been reported to be free from viruses, viroid, BLO, mycoplasma, bacteria and fungi (Bitters, W. P. and Murashige, T. 1967. A place for tissue culture in citrus research. Calif. Citrograph 52: 226, 228, 270-272, 304, 306; Navarro, L., Civerolo, E./L., Juarez, J. and Garnsey, S. M. 1991. Improving therapy methods for citrus germplasm exchange. In: Proc. Eleventh IOCV Conference, IOCV, Riverside, pp.400-408). Thus, it will result in production of clean stocks of citrus propagules unassociated with undesirable juvenile characters found in nucellars.
Efforts to culture shoot meristem of citrus started during mid sixties, but success could not be achieved (Murashige, T., Bitters, W. P., Rangan, T. S., Nauer, E. M., Roistacher, C. N. and Holliday, P. B. 1972. A technique of shoot apex grafting and its utilization towards recovering virus-free Citrus clones. HortScience 7: 118-119). Since then, despite concerted efforts made world over, success continued to elude citrus meristem culture. As an alternative to shoot meristem culture, micrografting as aseptically grafting shoot meristem of scion onto the epicotyl of a rootstock, has been resorted to in citrus, despite being very tedious and time consuming and requiring great skill and dexterity that too with only about 40% success (Murashige, T., Bitters, W. P., Rangan, T. S., Nauer, E. M., Roistacher, C. N. and Holliday, P. B. 1972. A technique of shoot apex grafting and its utilization towards recovering virus-free Citrus clones is described in HortScience 7: 118-119; Navarro, L., Roistacher, C. N. and Murashige, T. 1975). Improvement of shoot tip grafting in vitro for virus-free Citrus. is described in J. Amer. Soc. Hort. Sci. 100: 471-479; Navarro, L. 1992. Citrus shoot tip grafting in vitro is described in Biotechnology in Agriculture and Forestry, Vol. 18. Ed. Y. P. S. Bajaj, pp.327-338, Springer-Verlag, Berlin. Nevertheless, the micrografting experiments established that by employing meristems of citrus, viruses and other pathogens have been eliminated, resulting in increased fruit production Navarro, L., Civerolo, E. L., Juarez, J. and Garnsey, S. M. 1991. Improving therapy methods for citrus germplasm exchange is described in Proc. Eleventh IOCV Conference, IOCV, Riverside, pp.400-408.
The main objective of the present invention is to develop a method for production of viable and fertile Citrus plants through in vitro culture of 0.2 to 0.5-mm-long shoot meristems without intervening callusing.
Another objective is to provide growth media and sequential culture conditions, including the physical state of the substratum for optimum regeneration and proliferation of shoot meristems.
Still, other objective is to provide a method for rapid mass production of true-to-type and pathogen-free propagation stocks of both these important scion species.
Accordingly, the invention provides a method for regenerating viable and fertile Citrus plants culture from explants of field-grown mature trees of Citrus aurantifolia and C. sinensis, said method comprising the steps of:
a) cutting an explant from a Citrus plant selected from Citrus aurantifolia and C. sinensis said explant consisting of single-node stem segments from fresh shoots of field-grown mature trees,
b) decontaminating said explant by removing from its surface any contaminant which are harmful to the tissue culture process,
c) incubating the surface-sterilized explant at a temperature between 27xc2x0 C. to 30xc2x0 C. in the presence of ca.3 klux white fluorescent light for 15 hrs. a day, in agarified medium-A and B respectively for a period ranging between 20-30 days, to develop axillary buds and obtain 70-80% infection-free cultures,
d) subculturing the explant of step (c) along with sprouted axillary buds at least 4 times in medium A and B to produce several aseptic fast-growing shoots,
e) excising the meristem domes along with youngest 2-3 leaf primordia of length between 0.2-0.5 mm from the aseptically grown shoots and culturing said shoots in medium C at a temperature between 27xc2x0 C. and 30xc2x0 C. in the presence of ca.3 klux white fluorescent light for a period of about 15 days to generate shoots of length of ca. 8 mm,
f) subculturing the meristem-regenerated shoots on filter paper bridge employing liquid medium-D in order to obtain healthy shoots of an average length of about 1.5 cm without intervening callusing within a period of 20-25 days,
g) proliferating the meristem-regenerated shoots by repeated subculture in medium-A and medium-B, respectively to obtain an average of about 10 well-developed shoots within 4 subcultures of 30 days each,
h) rooting of the isolated well-developed shoots of C. aurantifolia to the extent of about 100% in 15 days, and of C. sinensis to the extent of about 90% in 25 days, in agarified media-E and F respectively.
i) transferring the freshly developed roots of C. sinensis to medium-G while allowing the shoots of C. aurantifolia to grow in the same medium for a further period of 15 days for development of tap roots,
j) hardening the rooted shoots ex vitro in the liquid medium-H for 10 days in a hardening chamber, wherein the relative humidity is regulated from high (ca. 90%) to gradually low (ca. 60%) under ca. 3 klux light intensity from white fluorescent tubes supplemented with light from incandescent lamps at 26xc2x0 to 28xc2x0 C. and allowing the shoots to grow in the same medium under incubation conditions for 30 days,
k) transferring the hardened shoot meristem-raised plants to soilrite in pro-trays for ex vitro growth at relative humidity of 90% to 60% at a temperature of 27xc2x0 C. to 30xc2x0 C. in the presence of white fluorescent light for a period of about 7 days to ensure 95% to 100% survival of the shoot meristem raised Citrus plants.
In an embodiment, the explant from a Citrus plant comprises shoot meristems of length of about 0.2 to 0.5 mm or single node stem segments.
In another embodiment, the explant is decontaminated by surface-sterilizing the nodal stem segments obtained from C. aurantifolia and C. sinensis, washing the said segments with tap water, followed by pre-treating with about 5% xe2x80x9cLabolenexe2x80x9d solution for 5 minutes, rinsing with distilled water followed by a quick dip in 95% ethanol and surface-sterilizing with 0.1% HgCl2 solution for about 15 minutes and washing the surface-sterilized nodal steam segments thoroughly with sterile distilled water followed by cutting off the affected internodal portions on either side of the node and preparing the explant for inoculation.
The Applicants hereby state that various culture media have been used in the method of for regeneration of citrus plants as described in the foregoing paragraphs.
The various media used in the process of the invention are described hereinbelow and represented in table 1. Accordingly, medium A comprises:
Further medium B comprises:
Medium C comprises:
Medium D comprises:
Medium E comprises:
Medium F comprises:
Medium G comprises:
Medium H comprises:
It would be pertinent to note that the various combination of the media hereinlisted would be apparent to those skilled in the art. Such media are deemed to fall within the scope of the present invention.
The tissue culture method for regenerating viable and fertile Citrus plants from field grown trees of C. aurantifolia and C. sinensis is described in further detail as under:
a) excising the single-node stem segments from fresh growth of shoots wherein the said method of field-grown mature elite trees of C. aurantifolia and C. sinensis during the month of February,
b) surface-sterilizing the nodal stem segments of both the Citrus species by washing the said segments with tap water, followed by pre-treating with about 5% xe2x80x9cLabolenexe2x80x9d, a neutral liquid detergent from Glaxo India Ltd. solution for 5 minutes, then rinsing with single distilled water followed by a quick dip in 95% ethanol and surface-sterilizing with 0.1% HgCl2 solution for about 15 minutes and washing the surface-sterilized nodal steam segments thoroughly with sterile distilled water followed by cutting off the affected internodal portions on either side of the node and preparing the explants for inoculation;
c) incubating the surface-sterilized explants of C. aurantifolia and C. sinensis under ca. 3 klux white fluorescent light for 15 h a day at 27xc2x0xc2x11xc2x0 C. temperature in agarified medium-A and medium-B respectively, for a period ranging between 20-30 days for axillary bud sprouting to obtain 70-80% infection-free cultures of C. aurantifolia and C. sinensis,
d) subculturing the explants along with sprouted axillary buds for at least 4 times in the same respective media as in step (c) to produce enormous number of aseptically fast-growing shoots,
e) excising the meristem domes along with youngest 2-3 leaf primordia ranging in length between 0.2-0.5 mm from the aseptically grown shoots followed by their culture on the liquid medium-C under the same controlled light and temperature conditions as in step (c) at least for a period of 15 days to let them attain a length of ca. 8 mm,
f) subculturing the meristem-regenerated shoots on filter paper bridge employing liquid medium-D in order to obtain healthy shoots of an average length of about 1.5 cm without intervening callusing within a period of 20-25 days,
g) proliferating the meristem-regenerated 1.5-cm-long shoots of C. aurantifolia and C. sinensis by repeated subculture in medium-A and medium-B, respectively to obtain well-developed shoots to the extent of an average 10 shoots and 6 shoots, respectively, within 4 subcultures of 30 days each,
h) rooting of the isolated well-developed shoots of C. aurantifolia to the extent of 100% in 15 days, and of C. sinensis to the extent of 90% in 25 days, in agarified media-E and F respectively.
i) transferring the just rooted of C. sinensis to medium-G while those of C. aurantifolia were left to grow in the same medium for a further period of 15 days in order to obtain almost a tap root-like system.
j) hardening the rooted shoots ex vitro in the liquid medium-H for 10 days in a hardening chamber, where the R.H. being regulated from high (ca. 900/%) to gradually low (ca. 60%) under ca. 3 klux light intensity from white fluorescent tubes supplemented with light from incandescent lamps at 27xc2x0xc2x11xc2x0 C. and allowing to grow the rooted shoots further in the same medium and incubation conditions for another 30 days.
k) transferring the hardened shoot meristem-raised plants to soilrite in pro-trays for ex vitro growth under the same humidity regime and incubation conditions as stated in step (j) for 7 days to obtain their 95% to 100% survival.
It took ca. 18 months to obtain well-developed healthy plants of an average height of 15 cm in potted soil, after the first establishment in aseptic culture of nodal explants taken from field-grown trees of Citrus.

Method for regenerating viable and fertile citrus plants by tissue culture from explants

Council of Scientific and Industrial Research