Method of making surface micro-machined accelerometer using silicon-on-insulator technology

A method of making a monolithic accelerometer which includes a sensor and associated signal conditioning circuitry, comprising:

• preparing a silicon-on-insulator (SOI) wafer, wherein the SOI wafer includes a substrate wafer, a silicon layer, and an oxide layer positioned in between the substrate wafer and the silicon layer;
• forming a buried layer for use in fabricating the signal conditioning circuitry in the silicon layer of the SOI wafer;
• defining a location for the sensor on the silicon layer of the SOI wafer;
• defining a location for a sensor trench in the silicon layer on each side of the defined sensor location;
• etching the sensor trenches on each side of the sensor location down to the oxide layer of the SOI wafer;
• filling the sensor trenches with polysilicon;
• processing the SOI wafer to form the signal conditioning circuitry;
• etching the polysilicon in the sensor trenches down to the substrate wafer;
• and
• etching the oxide layer surrounding the silicon layer in the defined sensor location.