A two-axis micromachined silicon actuator with micrometer range electrostatic actuation and picometer sensitive capacitive detection

This article presents an innovative micromachined silicon actuator. A 50-mu m-thick silicon foil is anodically bonded onto a broached Pyrex substrate. A free standing membrane and four coplanar electrodes in close proximity are then lithographied and etched. The use of phosphorus doped silicon with low electrical resistivity allows the application of an electrostatic force between one electrode and the moving diaphragm. This plane displacement and the induced interelectrode variation are capacitively detected. Due to the very low electrical resistivity of the doped silicon, there is no need to metallize the vertical trenches of the device. No piezoelectric transducer takes place so that the mechanical device is free from any hysteretic or temperature dependance. The range of the possible actuation along the x and y axis is around 5 mu m. The actual sensitivity is x(n)=0.54 Angstrom/Hz(1/2) and y(n)=0.14 Angstrom/Hz(1/2). The microengineering steps and the electronic setup devoted to design the actuator and to perform relative capacitive measurements Delta C/C=10(-6) from an initial value C approximate to 10(-13) F are described. The elaborated tests and performances of the device are presented. As a conclusion, some experimental projects using this subnanometric sensitive device are mentioned. (C) 2000 American Institute of Physics. [S0034-6748(00)04005-3].