Patent GB-1328707-A (GB)
Title: Semiconductive transducer
IPC: H01L29/00
Filed: 1971-04-19
Abstract: 1328707 Semi-conductors OMRON TATEISI ELECTRONICS CO 19 April 1971 [16 Nov 1970 20 Jan 1971] 22183/71 Heading H1K A mechanioal-electrical transducer (Fig. 1) comprises an N-type Si substrate overlain by insulant film 2 of SiO 2  deposited thermally or by pyrolysis of silane, or a film of Si 3 N 4 , SiO 2 +PbO or Al 2 O 3  + SiO 2 . A portion of the film is removed by photoetching to leave aperture 302, and a layer 3 of high conductivity SnO 2  is deposited e.g. by pyrolysis of (CH 3 ) 2 SnCl 2  or SnCl 4  vapour in air or O 2  carrier in a heated quartz reaction tube. Sb 2 O 3  may be admixed. P type Si, Ge or GeAs may be used as substrate. Electrodes 4, 4<SP>1</SP> of vacuum evaporated Ni are deposited on both surfaces of the substrate, and a metal or glass pressure needle 5 abuts on the SnO 2  layer, while reverse bias is applied between the electrodes through ammeter 7, whose reading of reverse current is approximately linear against applied pressure (Fig. 3, not shown). In a modification (Fig. 4, not shown) pressure may be applied through a ball, and the substrate surface of the transducer may advantageously be left uneven (Fig. 5, not shown), whereby a shearing stress is produced in the barrier, to produce improved characteristics (Fig. 6, not shown). A physical explanation is given. In a further modification (Fig. 7) the face of the substrate 51 is etched with a lattice of grooves 50 and insulant film 52 of e.g. Si 3 N 4  is applied to the ungrooved portions, and may serve as an etching mask. A film 53 of SnO 2  is deposited over the entire surface. The SnO 2  layer being transparent, the composite device may be photovoltaic to light applied to the barrier. If photosensitivity is not required, an opaque e.g. Ni, Mo, W, Pt, Cr layer is deposited on the SnO 2  layer in contact with the electrode. Alternatively a film of Al 2 O 3 , SiO 2  or Si 3 N 4  may be deposited thereon (Fig. 8, not shown). The SnO 2  layer may be deposited on a definite area and SiO 2  deposited thereon and around the same to receive the applied pressure (Fig. 9, not shown). Dual transducers 61, 62 may be formed on a single substrate with associated resistors 63, 64 by depositing SiO 2  on the substrate 1 and providing two openings over which SnO 2  is deposited, extending as a thin meandering strip over the insulant to operate as a definite resistor. Terminals 65, 66, 67 are provided and the assembly is conneotible as a bridge for operation e.g. with a balance (Fig. 10). Alternatively electrodes 65, 66 are series connected to an A.C. source and a single pressure is applied to both transducers, which operate as series opposed diodes. On each half cycle a forward current flows through one and a variable reverse current through the other so that the resultant A.C. is proportional to the applied pressure. Switchable polarity D.C. may also be used. In a further modification (Fig. 11, not shown) two transducers are respectively responsive to pressure and incident light, and (Fig. 12, not shown) the substrate comprises an N+ layer overlain by an N layer in which is formed a NPN transistor, and an interconnected pressure transducer.