Direct stress sensing by semiconductor elements has evolved recently. The element as originally introduced was a small piece of a semiconductor wafer serving as a diaphragm with electrical elements formed therein. This semiconductor diaphragm was then bonded to or mechanically coupled to a support structure which restricted motion of the periphery of the diaphragm with respect to its support structure, i.e. constrained the diaphragm by a peripheral surface in one of the diaphragm faces. However, poor bonding and differences between the thermal coefficients of expansion of the semiconductor material and the support structure material limited the accuracy of the composite structure as a stress sensor due to error stresses resulting from these coefficient differences.
It has been previously proposed that the support structure be made of the same material as the semiconductor diaphragm. Thus, the temperature coefficients of expansion in the semiconductor diaphragm and in the support structure would be equal. A method of making a stress sensor unit wherein the semiconductor diaphragm and the support flange are a single material unitary body is presented in U.S. Pat. No. 3,417,361 to H. B. Heller. It has been found that the stress sensor need not be a single material unitary body as shown in that patent if a joint between the semiconductor diaphragm and the support flange is formed by a strong bond.
Costs decrease if semiconducting material diaphragm-support structure units can be produced in a batch fabrication process. Uniformity of performance is also improved.
An object of this invention then is to provide a method to fabricate such stress sensors in a batch.