Improved all-silicon microcantilever heaters with integrated piezoresistive sensing

This paper presents the design, fabrication, and characterization of improved all-silicon microcantilever heaters with integrated piezoresistive sensing. The fabricated microcantilever heaters with piezoresistors are made solely from single crystal silicon with selective doping. Detailed characterization was performed to test the devices' electrical, thermal, and mechanical properties. The performance of and crosstalk between heater and piezoresistor elements were thoroughly tested. The resistive heater could reach temperatures of > 600 °C, and its temperature coefficient of electrical resistance was (2.01 ± 0.04) × 10^-3 Ω/Ω · °C. When biased at 2 V in a Wheatstone bridge, the deflection sensitivity of the piezoresistor was (4.25 ± 0.05) × 10^-4 V/V · μm and remarkably, the heater circuit had a measurable deflection sensitivity of (7.9 ± 0.5) × 10^-5 V/V · μm. Both the piezoresistor and the resistive heater were interfaced with a commercial atomic force microscope system to measure their sensitivities during topography imaging. The sensitivity of the thermal reading was much greater than that of piezoresistive reading. Noise-limited resolution of thermal reading was better than 0.46 ± 0.03 nm/√Hz and piezoresistive reading was better than 3.4 ± 0.4 nm/√Hz. This is the first experimental comparison between thermal and piezoresistive topographic sensing, both of which can replace optical lever sensing. Four cantilevers in an array demonstrated parallel topographic sensing with both the heater and the piezoresistor.