A silicon p-n junction transducer

A simple silicon p-n junction cantilever stress transducer is described. The device uses the anisotropic stress effect in p-n junctions. Previous designs use stylii or other additional members for applying force to small areas to achieve the necessary high stress concentration. The cantilever stress transducer achieves this by the proper geometry without additional members. The force concentration is achieved by a sharp notch immediately below the p-n junction. The cantilever is fixed on one side and the force applied to the other end. Bending occurs only in the thin area above the notch, thus creating the high stress. Sensitivity to bending is achieved only when mechanical damage is produced at the surface of the shallow junction in a controlled fashion. Diode reverse current of the p-n junction is increased by bending in one direction and decreased by bending in the other. The relationship between bending force and current change is linear up to 1,600 dyne-cm in either bending direction. The device responds to moments as low as a few millidyne-cm. No initial stress of the device is required. Results of the doping level (resistivity) on the sensitivity of the device are given. The device can be fabricated in various geometries and thus adjusted to different displacement values as well as sensitivities. A device of approximately 60 db signal-to-noise ratio has been constructed. Different applications for the device are discussed. Maximum sensitivity to date using this device configuration is 0.16 µa/dyne-cm-V.