the nanoribbon structure has recently been extensively investigated for many applications , such as zns nanoribbon lasers , graphene nanoribbon field - effect transistors ( gnrfets ) , nanoribbon sensors in si   and other materials . nanoribbon structures offer a relatively easy system to access , control and process , due to their relatively larger scale compared to other nanostructures , such as nanowires ( nws ) , nanodots ( nds )   and nanotubes ( nts ) . nanoribbons or thin silicon on insulators have many advantages , such as low leakage and a high on / off current ratio , ion / ioff , which leads to low power consumption while the device is inactive . in addition , since their parasitic capacitance is effectively eliminated by the underlying insulating layer , nanoribbon- or thin silicon - based devices have advantages for rf applications . such structures also have a lower threshold shift in response to temperature variations [ 10 - 13 ] . however , the reduction in mobility induced by the thermal scattering causes the operation points of the device to vary with the temperature . this temperature - dependent variation of the operation points makes the devices hard to operate properly .   for some high - temperature circuits , it is desirable that the individual devices have a specific operation point where the device characteristics show no variation with temperature . in this work , we demonstrate the feasibility of the constant operation of the fabricated devices in the temperature range from 25 to 150c . the method employed to achieve the constant operation of the fabricated devices , which is similar to zero temperature coefficients ( ztc ) , is based on the use of a substrate bias ( vsub ) . by accumulating or depleting the carriers on the channel surface using the substrate bias ( vsub ) , a 30-nm - thick p - type silicon on insulator ( soi ) wafer has been used as the starting material , and the soi layer has been thinned down to 20 nm by oxidation . the length lch and width wch of the channels , defined by conventional lithography , were 30 and 10 m , respectively . the thickness ( tox ) of the gate oxide was 40 nm , and n poly silicon was used as the gate electrode . au / al was used as the metal electrodes for the source , drain , gate , and substrate contacts . the electrical characteristics of the devices were measured by an hp4155b semiconductor parameter analyzer with a hot chuck for elevated temperature measurements . to diffuse the heat over the whole device at each temperature , schematic cross - section of fabricated nanoribbon fet we used a substrate bias ( vsub ) to ensure the constant operation of the devices at elevated temperatures , and the measurements were compared with the two - dimensional simulation results obtained from structures identical to those of the fabricated devices . in order to evaluate the substrate and top bias - dependent channel carrier modulation as a function of temperature , we extracted the channel cross - section profiles containing the on- and off - current density distribution at different temperatures . figure 2a shows the gate transfer characteristics of the fabricated ( solid lines ) and simulated ( dashed lines ) nanoribbon fet structures . the current level decreases as the temperature increases , which is ascribed mainly to the influence of lattice scattering caused by the elevated temperature on the mobility decay . figure 2b shows the decays in the normalized saturation current level and mobility values at different temperatures . both the simulated and measured current levels and therefore the mobility values follow the power - law decay behavior (  t ) . note that the mobility values presented in fig . 2 do not have a unit but instead show relative degradation ratio with respect to the room temperature value . such mobility degradation , where lattice scattering is the dominant scattering mechanism , can be expressed by a power law . this variation of the current level or mobility can make the device difficult to use in high - temperature or temperature - variable ambient applications . a measured ( solid line ) ( the dashed lines show the corresponding results obtained from the 2d numerical simulations ) . b the power law decay behavior of the normalized drain current and mobility as a function of temperature in the range from 25 to 150c to overcome such a thermal problem , which may result in the variation of the operation point , it is desirable to keep the current level constant over a range of temperatures . in order to realize such operation of the nanoribbon fets , we propose the following two methods of compensating for the variation in the current level with temperature from room temperature up to 150c ; ( 1 ) a suitable positive bias vsub is applied to realize this constant level operation , by enhancing the current level at elevated temperatures to the room temperature ( t ~ 25c ) current level , as can be seen in method  ( 1) of fig . 3a . ( 2 ) a negative vsub is applied to reduce the current level at different temperatures down to its level at t ~ 150c , as can be seen in method  ( 2) of fig . ( the dashed lines show the corresponding results obtained from the 2d numerical simulations ) . e show the channel cross - sections of the device , indicating the conduction current density contours for the on state b at room temperature and ct = 150c with vsub = 0 , and for the = 0 figure 3a shows the drain characteristics of the fabricated ( solid lines ) and simulated ( dashed lines ) nanoribbon fets as a function of temperature in the range between 25 and 150c . figure 3b , 3c , 3d and 3e show the channel cross - sections of the device , showing the conduction current density contours . figure 3b and c show the conduction current density contours for the  on state at room temperature and t ~ 150c , respectively . these two contour plots clearly indicate that the conduction current is reduced by the mobility degradation as the temperature increases . figure 4a shows the compensated ids  vds curves derived from the measurements ( solid lines ) and simulations ( dashed lines ) with a positive substrate bias vsub , according to  method ( 1). the inset shows the vsub values applied for the purpose of keeping the operation of the device constant for temperatures in the range from 25 to 150c . an approximately constant level on - state however , the maximum leakage current in the off state is as much as ~9% of the on - state current level . this is due to the additional inversion currents on the bottom of the channel surface formed by the positive substrate bias , vsub . as can be seen in fig . 4c , an increase in the current density , j , is clearly observed on the bottom of the channel surface . a compensated ids  vds curves with positive substrate bias ( vsub ) of the device . the inset shows the substrate bias ( vsub ) applied for the purpose of keeping the operation of the device constant for temperatures from 25 to 150c . ( the dashed lines show the corresponding results obtained from the 2d numerical simulations . ) b and c show the channel cross - sections of the simulated device , indicating the conduction current density contours for the compensated bon state and coff state with vsub = 15.1 v at t = 150c unlike in method ( 1 ) , where the complete off - state of the device is not achieved , method ( 2 ) uses a negative substrate bias , vsub . figure 5a shows the compensated ids  vds curves of the fabricated ( solid lines ) and simulated ( dashed lines ) devices with negative substrate bias ( vsub ) based on method ( 2 ) . the inset also shows the negative substrate bias ( vsub ) applied for the purpose of keeping the operation of the device constant for temperatures in the range from 25 to 150c . in contrast to method ( 1 ) , the off - state leakage current levels are drastically suppressed in the linear scale values of the drain currents . this is due to the negative vsub , which effectively depletes the carriers in the channel . 5b and 5c , where no significant inversion currents are observed on the bottom of the channel surface . a compensated ids  vds curves with negative substrate bias ( vsub ) of the device . the inset shows the substrate bias ( vsub ) applied for the purpose of keeping the operation of the device constant for temperatures from 25 to 150c . ( the dashed lines show the corresponding results obtained from the 2d numerical simulations . ) b and c show the channel cross - sections of the simulated device , indicating the conduction current density contours for the compensated bon state and coff state with vsub = 12.14 v at t = 150c table 1 compares the off - state drain leakage portion of the two methods at different temperatures . as shown in table 1 , in the case of method ( 1 ) , the off - state leakage portion measured at 25c is 0.28% , whereas method ( 2 ) shows clearly reduced values of 5.2  10 , suggesting that the leakage control is about five orders of magnitude better than that in method ( 1 ) . as the temperature increases , the leakage portion increases in both cases , but the leakage portion in method ( 2 ) is still one or two orders of magnitude smaller than that in method ( 1 ) at elevated temperatures of 125 and 150c . measured data shown as portion of leakage current levels ( ileak / ion ) in percentages ( % ) at different temperatures in summary , we report the constant temperature operation of nanoribbon fets in the temperature range of 25150c . in order to compensate for the variation in the current level with the temperature in the range from 25 to 150c , we propose two methods . the physical mechanisms are ; ( 1 ) to accumulate the lower part of semiconducting channel by applying a suitable negative substrate bias to enhance the total current level at elevated temperatures or ( 2 ) to deplete the lower part of the semiconducting channel by applying a positive substrate bias to reduce the total current level at lower temperatures . the leakage current level was drastically reduced by the negative substrate bias , as the carriers in the channel are effectively depleted , thus compensating for the fluctuating off - current level . although both approaches show constant on - state current saturation characteristics over the proposed temperature range , the latter shows an improvement in the off - state control of up to five orders of magnitude ( ~5.2  10 ) . these results were confirmed by two - dimensional numerical simulations , which show that the substrate bias causes the channel to be effectively depleted or accumulated . this work was supported by national research foundation of korea grant funded by the korean government ( 2009 - 0066544 and 2010 - 0015360 ) and the research grant of kwangwoon university in 2010 . this article is distributed under the terms of the creative commons attribution noncommercial license which permits any noncommercial use , distribution , and reproduction in any medium , provided the original author(s ) and source are credited . this article is distributed under the terms of the creative commons attribution noncommercial license which permits any noncommercial use , distribution , and reproduction in any medium , provided the original author(s ) and source are credited .
we experimentally demonstrated that nanoribbon field - effect transistors can be used for stable high - temperature applications . 
 the on - current level of the nanoribbon fets decreases at elevated temperatures due to the degradation of the electron mobility . 
 we propose two methods of compensating for the variation of the current level with the temperature in the range of 25150c , involving the application of a suitable ( 1 ) positive or ( 2 ) negative substrate bias . 
 these two methods were compared by two - dimensional numerical simulations . 
 although both approaches show constant on - state current saturation characteristics over the proposed temperature range , the latter shows an improvement in the off - state control of up to five orders of magnitude ( 5.2  106 ) .