Controlled Current Filaments in PNIPN Structures with Application to Magnetic Field Detection

T h e purpose of this paper is to show how P N P N structures can be biased stably to support controlled current filaments and to describe a sensitive magnetic field detector utilizing this principle in a P N I P N structure. P N P N devices are widely used as 2-terminal bistable switches 1 and as 3- and 4-terminal controlled switches, 2 and have also been utilized in 4-terminal operation as a linear amplifier. 3 The multiterminal circuit operation of the P N I P N structure described here forces 467 nearly equal base and emitter currents and thereby suppresses these switching and amplifying effects. Stable filament formation properties are introduced when significant spreading resistance is incorporated in each base layer. For the operating conditions considered, the central junction remains in reverse bias and supports counterflowing confined streams of both electrons and holes. The shape and position of this filament are controlled by fully characterized device and circuit parameters, in contrast with previously reported filamentary instabilities. 4 Magnetic field sensing is made possible because a magnetic field applied perpendicular to the filament displaces it laterally and thereby produces a signal in the external circuit. The displacement can be many times larger than the Hall displacement of either carrier species for a single transit of the I region. The I region is incorporated in the structure for the purpose of increasing filament length and hence its interaction with the magnetic field.