Characterization of a vertically movable gate field effect transistor using a silicon-on-insulator wafer

Abstract

The vertically movable gate field effect transistor (VMGFET) is a FET-based sensing element, whose gate moves in a vertical direction over the channel. A VMGFET gate covers the region between source and drain. A 1 μm thick air layer separates the gate and the substrate of the VMGFET. A novel fabrication process to form a VMGFET using a silicon-on-insulator (SOI) wafer provides minimal internal stress of the gate structure. The enhancement-type n-channel VMGFET is fabricated with the threshold voltage of 2.32 V in steady state. A non-inverting amplifier is designed and integrated on a printable circuit board (PCB) to characterize device sensitivity and mechanical properties. The VMGFET is mechanically coupled to a speaker membrane to apply mechanical vibration. The oscillated drain current of FET are monitored and sampled with NI LabVIEW. The frequency of the output signal correlates with that of the input stimulus. The resonance frequency of the fabricated VMGFET is measured to be 1.11 kHz. The device sensitivity linearly increases by 0.106 mV/g Hz in the range of 150 Hz and 1 kHz.

Double-gate thin film transistor with suspended-gate applicable to tactile force sensor

“…The pressure was applied using an insulated probe tip. The drain current in the saturation region of the suspended-gate TFT can be calculated from the following equation [17] where W and L are the channel width and length of TFT, V g and V t are the gate voltage and threshold (1) voltage, respectively; µ sat is the saturation mobility, and C t is the total capacitance of the insulator layers, which is expressed as [17]:…”

“…The pressure was applied using an insulated probe tip. The drain current in the saturation region of the suspended-gate TFT can be calculated from the following equation [ 17 ] where W and L are the channel width and length of TFT, and are the gate voltage and threshold voltage, respectively; is the saturation mobility, and is the total capacitance of the insulator layers, which is expressed as [ 17 ]: where and are the protective dielectric (alumina) and air gap capacitance, respectively. can be expressed as where , , A, and d gap are the relative dielectric constant of air, absolute dielectric constant, area of the gate of TFT, and air gap thickness, respectively.…”