Sensors and Actuators A, 39 (1993) 19-23 19 Investigation of the magnetosensitivity of a dual-emitter dual-base structure in oscillator mode of operation N. Smirnov, N. Nedev and A. Boursas Institute of Solid State Physics, Tsarigradsko chaussee 72, 1784 Sofia (Bulgaria) (Received November 8, 1991; in revised form November 13, 1992; accepted December 1, 1992) Abstract An oscillator circuit using a dual-emitter dual-base (DEDB) structure as an active element and having an oscillation frequency dependent on the magnetic field is presented. The emitters of the DEDB structure are externally connected and their current-voltage characteristics have a region with negative resistance. Thus an oscillating mode of operation may be achieved by the introduction of a capacitor between the emitters and the common base. The physical processes taking place in the device and the influence of a magnetic field on them in the oscillating mode of operation have been discussed. The absolute and relative magnetosensitivities of the DEDB structure may be varied in a wide range up to 800 kHz/T and 380 % T -I. 1. Introduction It is well known that the unijunction transistor (UJT) is widely used in relaxation oscillator trigger circuits [1]. This application is possible because the cur- rent-voltage characteristics of the UJT emitter exhibit a region with negative resistance. The change of the UJT emitter current caused by a magnetic field allows this device to be used as a magnetic-field sensor in a circuit with an a.c. output. Published results [2] show that the magnetosensitivity of such a sensor is 20 kHz/T. In a recent publication [3] a device with high magnetic- field sensitivity has been reported. This is the so-called dual-emitter dual-base magnetotransistor (DEDBMT), whose total emitter-current characteristics also have a region with negative resistance. In the present paper the results of using the DEDB structure as a magnetic- field sensor in a circuit with frequency output are presented. RE -];o~ ,Out Fig. 1. DEDB structure and the oscillator circuit. L1=240 ~m, L2=65 I.~m,L=300 ~m, W=50 /~m. 2. Device structure and oscillator circuit The dual-emitter dual-base structure and the oscil- lator circuit are shown in Fig. 1. The DEDB structure is similar to that of the DEDBMT [3] except for the absence of a collector, and will not be discussed in detail here. It has two bases B1 and B2 and two emitters E1 and E2. The latter are externally connected and a capacitor C is introduced between them and the common base B2. The first (El) and the second (E2) emitters are positioned on the upper surface in such a way that E1 begins to inject at a lower voltage VEB than E2. All the measurements are made in common B2 con- figuration and all potentials are measured relative to B2. The magnetic-field is applied parallel to the z-axis, i.e., perpendicular to the device cross section (B ÷ along the +z-axis, B- in the opposite direction). 0924-4247/93/$6.00 © 1993- Elsevier Sequoia. All rights reserved