CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the priority benefit of U.S.A. provisional application Ser. No. 60/759,170, filed on Jan. 12, 2006, all disclosures are incorporated therewith. This application also claims the priority of Taiwan application serial no. 95124777, filed Jul. 07, 2006. All disclosure of the Taiwan application is incorporated herein by reference. 


   BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   The present invention is related to a technology of bio-chip, and more particular to a bio-chip using the surface acoustic wave (SAW) mechanism, capable of detecting a bio sample. 
   2. Description of Related Art 
   The surface acoustic wave (SAW) technology has been used in wide application. According to its design mechanism, it can be used to detect various changes in physical or chemical properties, and can be used to design a detector for detecting, for example, temperature, pressure, twist, or even the volatile of gas or chemical material. 
   Certainly, the SAW apparatus can also be used in bio-chemical or biomedical detection. Due to the design with high sensitivity and simple structure, the SAW apparatus has been well considered in applications. Generally, the SAW apparatus needs to be covered with a bio-recognition coating layer for detecting the bio sample, such as a specific bio-chemical or biomedical material. 
   In the bio-chemical or bio-medical field, several type of biomarkers have been known to help the estimation or diagnosis of various diseases or the relating symptoms. As a result, the prevention or precaution on developing or worsening of diseases can be made. For example, the status of cardiovascular diseases can be estimated or diagnosed by using markers of CK-MB (CK, Myoglobin) and Troponin-I/T. If the Troponin-I/T is the sample to be detected, generally, since the concentration of Troponin-I/T in blood is very low, it therefore needs to be detected by a sensor with high sensibility. However, in the conventional technology, the detecting sensibility for the Troponin-I/T is relatively low. This conventional technology for detecting the Troponin-I/T still has disadvantages to be further solved. 
   Reviewing the prior art, U.S. Pat. Nos. 6,321,588; 5,306,644; and 5,992,215 have disclosed relating detection tools in combination with SAW for signal amplification. The signal is then detected by circuit. These prior arts are concentrating on analyzing the chemical material and gas molecules. Although the U.S. Pat. No. 4,598,224 also discloses a relating technology but the quantity analysis and noise treatment are not considered. The publications or published patents are generally on the application of communication and high frequency device but not on the application of bio-sensor. In addition, some of them may be used to detect the micro change in physical quantity, such as analysis of existence of gas or chemical material in small quantity. 
   In addition, the conventional SAW apparatus can use, for example, the Inter-Digital Transducer (IDT) design. The publication of “The 30 th  Annual Conference of the IEEE Electronics Society, Nov. 2-6, 2004, Busan, Korea; pp 1546-1549” by Gi-Beum Kim et al. has also introduced the SAW sensor. The SAW sensor includes the IDT&#39;s on a piezoelectric substrate. The IDT&#39;s are formed from thin metal film. When an electric signal with appropriate frequency is applied to the input IDT, SAW is launched on the surface of the substrate due to the reverse piezoelectric effect. The SAW propagates across the surface of the substrate and is converted back into an electric signal by the output IDT. The operating frequency f, is determined by the IDT finger spacing ω s , finger width ω f , wavelength λ, and SAW velocity ν s  according to the relation of f=ν s /λ where λ=2(ω s +ω f ). The SAW velocity However, if a mass load is disposed on the path of the SAW, the SAW velocity ν s ∝√{square root over (c/ρ)} is proportional to the elasticity and density of the substrate and the associated mass load on it. Therefore, the mass load can be detected. The detail can be referred to Gi-Beum Kim et al. and can be understood by the person with ordinary skill. The further detail is omitted here. 
   However, due to the improper implementing structure of IDT in the SAW apparatus, the performance is not good and could be affected by the noise and echo phenomenon, and then the discerning capability and sensitivity get low. Since the quantity analysis in micro-amount is strongly needed in the current trend, it is strongly desired to have high precision with the least amount of sample. 
   The conventional design of IDT sensor has many disadvantages, such as easily producing noise. Since the IDT is very sensitivity, the surface is easily affected resulting in several issues. For example, the IDT cannot be integrated into an integrated circuit and it is not easy to handle on property under batch production. As a result, the development is quite limited. In these reasons, some experts in this field change the concerning point and develop the applications of SAW technology on the electronic filter. This technology has been developed for about half century. The efforts from experts on developing this technology are not much in recent years. However, based on the IDT mechanism, the bio-chip with better performance is still needed in continuous development. 
   SUMMARY OF THE INVENTION 
   Generally, the present invention uses the SAW device to have further applications on, for example, biomedical and bio-chemical detection, and pharmacology application such as the selection of target medicine. 
   The present invention uses a SAW bio-chip, having a SAW device with a sensing region and a signal processing circuit on a substrate. 
   In the present invention, a SAW bio-chip, which can amplify the signal different and filter the noise. 
   In the present invention, a testing sample region and a referencing sample region are provided under the same background conditions in measurement. By input from single acoustic signal generator, the testing sample region and the referencing sample region are arranged in symmetrical implementation, such as left-right symmetry. By detecting the difference between two signals from the testing sample region and the referencing sample region, the discerning precision with respect to the reference sample can be improved. 
   In the present invention, an absorption region can be located at the corresponding periphery of the SAW device. Under proper design and selection on material and size of the absorption region, the echo can be effectively absorbed or cancelled. 
   The present invention provides a SAW bio-chip, including a substrate having a property of piezoelectric material. An insulating layer is implemented on the substrate. A SAW generating region is implemented on the insulating layer, wherein a first SAW signal and a second SAW signal, being substantially identical, are generated by interaction with the substrate and travel on the insulating layer. A first SAW transduction region is implemented on the insulating layer to receive the first SAW signal for producing a first electric signal. A second SAW transduction region is implemented on the insulating layer to receive the second SAW signal for producing a second electric signal. When the bio-chip is in operation, a reference sample and a testing sample are disposed on the insulating layer and respectively on the routes of the first SAW signal and the second SAW signal. The two routes are symmetric with respect to the SAW generating region. 
   The present invention also provides SAW bio-chip, including a substrate having a property of piezoelectric material. An insulating layer is implemented on the substrate. A first Inter-Digital Transducer (IDT) unit is implemented on the insulating layer, wherein a first SAW signal and a second SAW signal, being substantially identical, are generated by interaction with the substrate and travel on the insulating layer. A second IDT unit is implemented on the insulating layer to receive the first SAW signal for producing a first electric signal. A third IDT unit is implemented on the insulating layer to receive the second SAW signal for producing a second electric signal. When the bio-chip is in operation, a reference sample and a testing sample are disposed on the insulating layer and respectively on the routes of the first SAW signal and the second SAW signal. The two routes are symmetric with respect to the SAW generating region. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
       FIG. 1  is a cross-sectional view, schematically illustrating a structure of SAW bio-chip, according to an embodiment of the present invention. 
       FIGS. 2A-2B  are top view and cross-section view, schematically illustrating a structure of SAW bio-chip, according to an embodiment of the present invention. 
       FIG. 3  is a circuit diagram, schematically illustrating the circuit structure of the SAW bio chip, according to another embodiment of the present invention. 
       FIGS. 4A-4C  are cross-sectional views, schematically illustrating a fabrication process for a SAW bio-chip, according to an embodiment of the present invention. 
   


   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention proposes a SAW bio-chip, capable of improving quantity precision in detecting a bio sample, in which the noise and the echo signal can at least be reduced. The present invention further uses a reference sample for producing a reference signal, so as to measure the signal difference of the measuring signal from the testing sample. As a result, under the same operation condition, the error in conventional method, caused by the separating measurements with different background conditions, can be reduced. Further, the noise and the residual echo of the acoustic signals can be further reduced by a filter and an acoustic absorbing structure. The precision can be further improved. In addition, since the measured quantity is the difference between the testing sample and the reference sample, the difference can be quantified, so as to determine the probability about whether or not the testing sample is the same as the reference sample. Some embodiments are provided for descriptions but the present invention is not just limited to the embodiments. 
     FIG. 1  is a cross-sectional view, schematically illustrating a structure of SAW bio-chip, according to an embodiment of the present invention. In  FIG. 1 , a substrate  100  is divided into a middle region  120  and two side regions  110  at a symmetrical arrangement with respect to the middle region  120 . The substrate  100  includes the property of piezoelectric material. For example, the substrate  100  is a block layer of piezoelectric material, or a structural block layer having a piezoelectric layer disposed on a bottom layer. The middle region  120  can be implemented with a SAW generating structure, such as an IDT structure, capable of converting an alternative electric signal into surface acoustic wave based on the piezoelectric property of the substrate  100 . For example, the surface acoustic waves are generated and travel in two opposite directions as shown by the wavy arrows. An insulating layer is implemented between the substrate  100  and the IDT unit, for isolation and serving as a wave guide layer. As a result, the physical wave generated from the middle region  120  can propagate out. This physical wave in the present invention is called surface acoustic waves  116  and  118 . The two side regions  110  are also implemented with the IDT units for respectively receiving the two surface acoustic waves  116  and  118  in two directions. In order to have better comparison effect, the middle regions is distant to the two side regions  110  in equal distance, and the IDT units at the two side regions  110  are identical, so as to again convert the received SAW signals into the electric signals for analysis. In other words, the two side regions  110  corresponding to the single middle region  120  have the symmetrical routes, preferably a symmetrical disposition in left-to-right symmetry. Certainly, the two side regions with respect to the middle region  120  may have an including angle. However, the two routes for the two side regions  120  to the middle region  120  are still in symmetric arrangement. 
   In operation, for example, a position at the left side of the middle region  120  can be disposed with a reference sample  112 , such as a bio reference sample. At the same time, a corresponding position at the right side of the middle region  120  can be disposed a bio testing sample  112 , such as a bio sample to be detected. Further, for example, the foregoing positions of the bio reference sample  112  and the bio testing sample  114  can be exchanged. The changes, when the SAW passes the bio testing sample and the bio reference samples, can be simultaneously measured by the IDT units at the two side region  110 . Since the operation condition are the same, the measured signals from the IDT unit at the two side regions  110  can be, for example, analyzed in difference. This can at least reduce the error caused in conventional method by separating measurement under different operation conditions. The structure of SAW bio-chip is to be described in further detail as follows. 
     FIG. 2A  and  FIG. 2B  are top view and cross-section view, schematically illustrating a structure of SAW bio-chip, according to an embodiment of the present invention. In  FIG. 2A  and  FIG. 2B , an insulating layer  230  is formed on a substrate  200 , and also serves as a wave guide layer, called SAW propagation layer. The substrate  200 , as previously described, is a substrate having the property of piezoelectric material. In  FIG. 2A  and  FIG. 2B , a piezoelectric layer is taken as the example for description. The middle region  220  of the insulating layer  230  is formed with SAW generating structure  240   a.  Via the medium of the insulating layer  230 , a first surface physical wave  116  and a second surface physical wave  118  being substantially identical are generated, and preferably propagating in two opposite directions. The SAW generating structure  240   a  is, for example, a pair of metal bar layers, that is, IDT unit. The two terminals  280  of the SAW generating structure  240   a  can be applied an alternative electric signal to the IDT unit. The alternative electric signal can be, for example, a period wave such as semi-period wave, sine wave, square wave, triangle wave. The generated electric field would generate the stress on the piezoelectric material, so as to produce the SAW. Further, according to the geometric shape of the metal bar layer, such as the length, width, bending gap, and size with the piezoelectric property of material, a specific propagation mode of the SAW can be generated. 
   Further, another two identical SAW transduction structure  240   b  and  240   c  are implemented on the insulating layer at the two side regions  210 , so as to receive the two SAW signals and convert them into two electric signals, which are output at the terminal  280 . In addition, after the SAW signals pass the SAW transduction structure  240   b  and  240   c  at two side regions  210 , it may have residual SAW signals in continuous propagation. In this situation, for example, an acoustic absorbing structure  250  can be additionally implemented, so as to avoid the improper reflection (or called echo) from the SAW signals in the insulating layer, causing measurement error. 
   When the bio-chip is in operation, the reference sample can be disposed on one of the two routes of the SAW signals, such as the position of the reference sample region  260 , by a contact layer. In addition, the testing sample can be disposed on another one of the routes of the SAW signals, such as the position of the testing sample region  270 . It preferably has the same distance for the position of the reference sample region  260  and the position of the testing sample region  270  in corresponding to the position of the SAW generating structure  240   a.  As a result, when the reference sample is compared with the testing sample in measuring difference, most of system error can be removed due to the operation condition being substantially the same. 
   It can be noted that the reference sample and the testing sample are disposed on the insulating layer  230 . Further, the SAW generating structure  240   a  is used to generate the SAW signals while the SAW transduction structures  240   b  and  240   c  are used to receive the measuring SAW signals. Here, the SAW generating structure  240   a  and the SAW transduction structures  240   b,    240   c  can be, for example, designed by the IDT structure. However, the other mechanism with similar function can be use, too. The present invention is not limited to the IDT design. 
   In addition, generally, the three regions  210 ,  220  are preferably arranged in a straight line and symmetry. However, this is not the only way in arrangement. It can be modified into other arrangements while the reference sample and the testing sample can be measured under the operation condition. For example, the three regions  210 ,  220  are not necessary to be in straight line. Further, according to the design by implementing the IDT unit at the region  220 , if the SAW signal is generated in isotropic direction, such as the structure in circular shape, then several side regions  210  with respect to the middle region  220  can be set, and several testing samples can be measured at the same time. The present invention proposes the comparison between the testing sample and the reference sample, such as the analysis on difference, so as to quantify the measured results. Under this principle, various designs can be made and it is not necessary to restrict to a specific design. 
   Continuously, the signals measured by the SAW transduction structures  240   b,    240   c  can be further processed and analyzed.  FIG. 3  is a circuit diagram, schematically illustrating the circuit structure of the SAW bio chip, according to another embodiment of the present invention. In  FIG. 3 , the signals measured from SAW transduction structures  240   b,    240   c  can be, for example, processed and analyzed by using external circuit in association with computer system. However, in order to have convenient use in bio-chip, a portion of circuit can be formed on a substrate  300 . 
   In  FIG. 3 , in addition to the structure as described in  FIGS. 2A-2B , a portion of circuit structure can be also formed on the substrate  300 . In other words, the implementation of the circuit structure allows the bio-chip itself already carries a signal processing circuit, so as to have convenient use. However, the circuit structure is not absolutely necessary to be formed on the substrate  300 . In other words, the bio-chip can, for example, output the electric signals to the external circuit unit for processing. In the following example for descriptions, a portion of the circuit is formed on the substrate  300 . For example, a conducting wire structure  380  and the SAW sensor  310  lead the output signals from the SAW transduction structures  240   b,    240   c  at the side region  210  to a differential amplifier  320 . The SAW sensor  310  and the differential amplifier  320  can be integrated into a circuit unit  325 . The differential amplifier  320  can take out the signal difference between the testing sample and the reference sample and properly amplifies the difference. Alternatively, the differential amplifier  320  can be a subtracting device for subtracting the two input signals. After the differential amplifier  320 , according to the actual need, the signal is further input to a signal processing unit  330  and a filter  340 . The signal processing unit  330  can further adjust the signal or even digitized the signal, and so on. The filter  340  can filter the noise. In other words, some signal processing circuits can be pre-formed on the substrate  300 . The signal can be output at the terminal  350  for the analysis by the external computer system  370 . The computer system  370  may need to process several bio-chips at the same time, wherein an interface of multiplexer  360  can be used to select the one to be analyzed. However, the foregoing analysis is just the example for the subsequent analyzing and processing, the process flow is not necessary to be the same as the embodiment. 
   In addition, form the fabrication point of view, for example, the semiconductor fabrication process can be used, including deposition, photolithography, etching, and so on. Further for example, the IDT unit at the regions  210 ,  220  can be patterned at the same time, so as to obtain the desired structure. The detail can be understood by the one in ordinary skill and is not further described. 
   In the following descriptions, an example for fabricating the  FIGS. 4A-4C  are cross-sectional views, schematically illustrating a fabrication process for a SAW bio-chip, according to an embodiment of the present invention. In  FIG. 4A , substrate  400 , such as ST-Cut Quartz with the piezoelectric property, is provided. A metal layer, such as gold layer, is formed and patterned by photolithographic and etching processes on the substrate, so as to form the IDT  402 . Here, the direction of the crystal lattice needs in consideration. In  FIG. 4B , an insulating layer such as silicon oxide layer is deposited over the substrate  400 . The insulating layer is, for example, 1 micron in thickness. In  FIG. 4C , another metal layer, such as gold layer, is formed and patterned by photolithographic and etching process to form the metal layer  406  on the insulating layer  404  to serve as a contact layer for adapting the sample. 
   Remarkably, the elements of surface Love wave usually have advantages of low attenuation and high sensitivity. However, the surface Love Wave is not always generated by any kind of layered structure. In order to generate the surface Love wave for the need of SAW, it needs the wave guiding layer on the substrate. The usual material for the wave guide layer can be silicon oxide, zinc oxide, or PMMA, in which silicon oxide is preferred because of low wave loss and resistance in alkalinity and acidity. In other words, the insulating layer  404  also servers as the wave guiding layer for the SAW. 
   The SAW bio-chip of the present invention has the analysis in high quality and quantity. The acoustic wave is converted in to AC output by the IDT. The IDT, the insulating layer and the structures at the regions of testing sample and reference sample can be formed by film deposition. The testing sample can be chemical product, food, agricultural product, or bio sample. The physiology analytes or bio sample can be blood, plasma, saliva, cerebral spinal fluid, lymph, urine, immunoglobulins, the immunoglobins complementary analytes, viruses, therapeutic drugs, hormones, proteins, steroids, neurotransmitters, receptors, glycosylated proteins, carbonhydrates, neucleic acids, cells, cancer markers, neucleotides, or heptens. 
   When the AC signal is input, the input terminal is connected to the periodic wave in fix frequency. The selection of the periodic wave can be adjusted according to the substrate, the insulating layer, and the IDT in a distance and width. The periodic wave with fix frequency can be semi-period wave, sine wave, square wave, triangle wave and so on. The alternating electric field can be generated between the electrodes. The piezoelectric crystal in responding to the electric filed produces deformation, so that the electric energy is converted into acoustic energy. Further, the signal passes the testing sample and the reference sample and the signals frequency is changed due the mass effect. Then, the signal processing circuit output the changes acoustic signal and convert the acoustic signal into the electric signals, which are further amplified and filtered in noise, and then output for the external measurement. 
   According to the preferred embodiment of the present invention, the signal difference between the testing sample and the reference sample is collected, so as to obtain the result. In the present invention, the noise and the echo between phase and phase can be significantly reduced by the design at the absorption region in material and size, and a symmetric design for the sample region (testing sample region and reference sample region) of the bio-chip. In addition, since the film deposition is used to form the sample regions, the amount of the samples in detection can be reduced. Since the only small amount of the sample is needed, the precision and the subsequent management and analysis on signal can be simplified and more quantified, so as to improve the competition on chip performance. 
   The present invention employs the proper symmetry design for the absorption region, the IDT with selected material and size under test and specific design, and the symmetric design for the testing sample region and reference sample region. Further, the structure formed by the fabrication process allows the simultaneous measurements for the testing sample region and reference sample region. As a result, the key factors of insufficient analyses in quantity and quality for the conventional method can be overcome by the present invention. The insulating layer can be formed by film deposition process. The signal processing circuit and the absorption region surrounding at the symmetric periphery of the SAW bio-chip can together reduce the noise and echo. The quantity analysis can be done by the differential circuit to discern the signal difference, and the signal can be amplified by signal processing circuit. In order for adapt various physiology analytes, they can be adapted by simply changing the materials at the sample regions. 
   It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing descriptions, it is intended that the present invention covers modifications and variations of this invention if they fall within the scope of the following claims and their equivalents.
A surface acoustic wave (SAW) bio-chip is designed with signal processing circuits. The chip can achieve precise measurements or detection quantitatively via the difference between the experiment-control mode, and followed by amplification and filtering of the signal processing circuits. By changing the designs of the substrate, quantitative detection toward different analyses can be achievable.