Zero displacement microelectromechanical force sensor using feedback control

Conventional microscale force sensors use moving parts to infer applied forces. Whenever physical deformations are involved, the sensor characteristics become a function of mechanical parameters, and there is an inevitable trade-off between the sensitivity and measurement range. We developed a microfabricated force sensor that uses feedback control to nullify any displacements within the device, directly transducing forces as high as 1.5 mN with a 7.8 nN resolution. The range and sensitivity of the device no longer depend on mechanical parameters, which allow the same device to be used to test samples with a wide range of stiffnesses without loss of accuracy.