Abstract
Nanosensitive mechanical microprobes with CMOS transistors, inverters, inverters cascades and ring oscillators, integrated on the thin silicon cantilevers are presented. Mechanical stress shifts linear, steep switching fragment of the inverters’ electrical characteristics. Microprobes were fabricated with use of the standard CMOS technology (3.5 μm design rules, one level polysilicon gate and one level of the metal interconnections) and relief MEMS technique. Control of the silicon cantilever thickness was satisfactory in the range above the few micrometers. Several computer simulations were done to analyze and optimize transistors location on the cantilever, in respect to the mechanical stress distribution. Results of the microprobes electromechanical tests confirm high deflection sensitivity 1.2 - 1.8 mV/nm and force sensitivity 2.0 - 2.4 mV/nN, both in nano ranges. Microprobes, with the ring oscillators revealed sensitivities 5 - 8 Hz/nm. These microprobes seem to be appropriate for applications in precise chemical and biochemical sensing.
Highlights
Silicon microcircuits with piezotransistors placed on the cantilevers enable precise measurements of mechanical parameters - deflection in the nm range and force in the nN range
Sensors with the individual MOS transistors, individual inverters, cascades of inverters and ring oscillators located on the elastic silicon cantilevers reveal higher sensitivity and better resolution than standard piezoresistor bease devices
Ring oscillator placed on the thin cantilever converts mechanical deflection/force into the resonant frequency shift
Summary
Silicon microcircuits with piezotransistors placed on the cantilevers enable precise measurements of mechanical parameters - deflection in the nm range and force in the nN range This feature opens several new application possibilities and widens existing ones in the areas of mechanical and biochemical sensing of the MEMS-type devices. Sensors with the individual MOS transistors, individual inverters, cascades of inverters and ring oscillators located on the elastic silicon cantilevers reveal higher sensitivity and better resolution than standard piezoresistor bease devices. These devices may be applied in AFM, SNOM systems and in biochemical analytical units with mass increment detection – increment which is caused by the molecules adsorption in the chemically active layers over the cantilever surface. This format of the output signal may be advantageous over the analog voltage/ current output signals from piezoresistive devices
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