Development of Biosensor Arrays Based on FETs

Due to their advantages over conventional optical arrays, electronic biosensor transducers and arrays have attracted intensive research interest in recent years. The vast majority of those efforts, however, are focused on the use of FETs as transducers and only a few groups have successfully prototyped their array devices [46-54]. The obvious reason for this is the high cost of mask making and chip fabrication. Among them, the CMOS process dominates due to the easy access to commercial CMOS foundries. 

In another report, a DNA sensor array of 16 x 8 sensor elements with pitch size of 250 pm has been fabricated using a 0.5—pm CMOS process [50, 51, 55]. The DNA h34 ridization is measured through the change of interfacial capacitance and then converted to a digital output signal by the integrated electronics. The chip was post-processed with a gold layer to facilitate the attachment of probe DNA 

Other examples of CMOS-based field-effect sensor arrays are used for the monitoring of extracellular electroph iological signals or pH changes [56]. Those devices normally involve only ISFETs and hence are less complicated in structure than those required for DNA or protein arrays. 

The aforementioned examples with CMOS processes achieved success to a certain level, either in the electronic performance or in measurements with actual biological samples. However, due to the different fabrication factors, applications and characterization methods, it is impractical to compare the performance of the biosensor arrays. 

The use of TFTs in electronic biosensor array is still limited. Various TFT-based DNA and protein transducers have been developed either with poly-Si or amorphous silicon TFTs [4,58]. Although proved to be successful as sensor transducers, working TFT-based sensor arrays have not reported in the literature. This is largely attributed to the fact that TFT foundries are mostly specialized for the manufacturing of LCD backplanes and not commercially available to researchers. 

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