Simulation Study of Sensitivity Performance of MEMS Capacitive Bending Strain Sensor for Spinal Fusion Monitoring

Table 1

Capacitive strain sensor comparison.

Application	Automobile tire strain monitoring	Rotating shaft surface strain	Spinal fusion monitoring	Spinal fusion monitoring
Design structure	Comb drive	Comb drive	Comb drive	Double layer cantilever
Sensing mechanism	Electrodes gap manipulation using flexible epoxy resin	Electrodes overlap area manipulation	Electrodes gap and overlap area manipulation	Electrodes gap manipulation
Sensitivity	45.71 aF/𝜇𝜀	255 aF/𝜇𝜀	2.94 fF/𝜇𝜀 (0–1000 𝜇𝜀)	0.02 pF/𝜇𝜀 (0–1000 𝜇𝜀)
Nominal capacitance	3.4–34.7 pF	440 fF	8.01 pF	18–43 pF
Output pattern	Nonlinear	Linear	Nonlinear	Nonlinear
Minimum gap	0.5 mm	2 μm	25 μm	3 μm
Sensor material	Flexible substrate (copper with polyimide) on ultra flexible epoxy resin	SOI wafer for substrate and device layer, aluminum electrode	Silicon boron doped very low resistivity; anodic bonding to borosilicate glass	Borosilicate glass, silicon p-type, gold electrodes