A controllable fabrication improved silicon nanowire array sensor on (111) SOI for accurate bio-analysis application

Silicon nanowire field-effect transistor (SiNW-FET) sensors possess the ability of rapid response, real-time, and label-free detection with high sensitivity and selectivity in the analysis of charged molecules. Their nano-scale size makes them well suited for ultralow detection of charged molecules, but also brings the uniformity fabrication challenging, thus limiting their large-scale application. By a horizontal control approach, highly controllable silicon nanowires arrays at the top of the silicon-on-insulator (SOI) wafer (T-SiNW) were developed in our previous work. To further improve the device uniformity, here a novel SiNW fabricated approach was carefully designed by the combination of horizontal and vertical control. The new silicon nanowires appeared at the bottom of the top silicon layer (B-SiNW). The B-SiNW has a relatively low requirement on the fabrication process and better device uniformity compared to T-SiNW. These improvements resulted in the B-SiNW device with a lower current fluctuation (4.1 nA with 5.1% variations) in the flowing liquid, compared to the T-SiNW device (4.4 nA with 11% variations). Further, in quantitative detection of 40 ng/mL MMP-9, the B-SiNW sensors provided larger signals and lower fluctuation (normalized average response value: 0.57 with 4.2% variations), compared to the T-SiNW sensors (0.41 with 12.1% variations), thus indicating a more accurate bio-analysis application of the B-SiNW sensor. This work advances the nanowire sensor technology a step closer toward large-scale application to create stable sensing platforms in disease diagnosis and monitoring.