Piezo-response of lateral bipolar transistors

The influence of mechanical stresses upon the offset of merged lateral bipolar magnetotransistors (LMTs) is studied. The experimental setup for analyzing the response of such structures to torsional and flexural stresses is briefly described. It has been found that their sensitivity to torsional stresses is much higher than to flexural stresses, and this may be explained in terms of the piezojunction effect which gives rise to emitter injection modulation (EIM), a phenomenon analogous to the one previously reported to explain the magnetic response of some types of LMTs. Other analogies between the response to mechanical stresses and to a magnetic field are described. Two different modes of electrical connections of the four collectors of the device are analyzed: cross-coupled and parallel. The parallel connection allows some degree of compensation of the offset due to torsional stresses, whereas the cross-coupled one is more sensitive to flexural stresses. It is concluded that: (1) the response to a magnetic field and a mechanical stress have many common aspects; (2) the piezojunction effect is the fundamental mechanism behind the measured sensitivity; and (3) these devices are potentially excellent stress sensors. (C) 1998 Elsevier Science S.A.