A magnetic field sensor is an entrance transducer that converts a magnetic field into an electronic signal. Semiconductor magnetic field sensors exploit the galvanomagnetic effects due to the Lorentz force on charge carriers. Integrated semiconductor, notably silicon, magnetic field sensors, are manufactured using integrated circuit technologies. Integrated sensors are being increasingly developed for a variety of applications in view of the advantage offered by the integration of the magnetic field sensitive element together with support and signal processing circuitry on the same semiconductor chip. The ultimate goal is to develop a broad range of inexpensive batch-fabricated high-performance sensors interfaced with the rapidly proliferating microprocessor. This review aims at the recent progress in integrated silicon magnetic devices such as integrated Hall plates, magnetic field-effect transistors, vertical and lateral bipolar magnetotransistors, magnetodiodes, and current-domain magnetometers. The current development of integrated magnetic field sensors based on III-V semiconductors is described as well. Bulk Hall-effect devices are also reviewed and serve to define terms of performance reference. Magnetic device modeling and the incorporation of magnetic devices into an integrated circuit offering in situ amplification and compensation of offset and temperature effects are further topics of this paper. Silicon will continue to be aggressively exploited in a variety of magnetic (and other) sensor applications, complementary to its traditional role as integrated circuit material.

Integrated semiconductor magnetic field sensors

Gallium arsenide Hall devices have been fabricated with very thin active layers formed by silicon implantation. The variation of Hall voltage with calibrated magnetic-flux density shows that the linearity error is better than ±0.03 percent in the magnetic-flux-density range below 10 kG at room temperature. Measurements in a superconducting magnet at 4.2 K shows that the linearity error is within ± 0.6 percent at the range below 68 kG. When this device is used as a magnetic sensor, magnetic-flux meters with an accuracy of 0.1 percent ( B B < 68 kG) at 4.2 K can be achieved.

Highly linear GaAs hall devices fabricated by ion implantation

A technique for the liquid‐phase epitaxial growth of thin GaAs layers has been developed. This technique uses supercooled solutions free from GaAs precipitates. With the amount of the initial supercooling in the range of 1–10 °C, very smooth surfaces with a roughness smaller than 0.01 μm are obtained for layers thinner than 1μm. The layer thickness data agree well with the diffusion theory equation by assuming that the diffusion coefficient of As in Ga is 4×10−5 cm2/sec at 800 °C. The thickness uniformity within a wafer is better than ±5%, and the thickness reproducibility among different runs is within ±7%. The carrier concentration is also well controlled.

Liquid-phase epitaxial growth of thin GaAs layers from supercooled solutions

Dual species ion implants of Se in conjunction with Ga implant in Cr-doped semi-insulating GaAs have been carried out. Electron concentration and mobility profiles have been investigated for annealed samples using differential Hall-effect and sheet-resistivity measurements. It has been shown that the dnal implantations give high maximum electron concentrations above 1 × 1019 cm−3 when those samples are annealed at 950°C using a low oxygen content CVD Si3 N4 encapsulant. Experimental results indicate that the major part of the enhanced maximum electron concentrations arise from Se donors on As vacancy sites.

Dual species ion implantation in GaAs

A double epitaxial gallium arsenide tuning diode has been developed for TV varactor tuners. The capacitance variation ratio is 6.0 and is large enough to cover the UHF TV broadcasting band. Diode series resistance is 0.18 Ω ( Q = 200 ) at 470 MHz, and at a capacitance of 9 pF. This resistance is 4.4 times smaller than Si diodes in its mean value. Contribution of each resistance component to the total diode resistance was studied. The result shows that package loss is 0.11 Ω, RF skin-effect resistance is 0.05 Ω, and the undepleted epitaxial layer resistance is 0.048 Ω. Therefore, a diode with a 0.075-Ω ( Q = 480 ) series resistance at 470 MHz could be developed, if package loss and RF skin-effect resistance are improved.

High-Q GaAs varactor diodes

Gallium-arsenide Hall-effect devices were developed by using Se-implanted n layers. A Hall voltage of 85 mV was generated at I = 1 mA and B = 5 kgauss. The imbalance voltage appearing was below 1.4 mV at I = 1 mA and B = 0.This fabrication technique is very promising in the high throughput of GaAs Hall-device production.

GaAs Hall-effect devices fabricated by ion-implantation technique

The design and fabrication of a GaAs varactor diode for u.h.f. t.v. tuners were carried out using a GaAs double epitaxial layer. The capacitance ratio of diode. C3/C25, is 6.0 and the series resistance at 470 MHz is 0.24 Ω. These characteristics are much better than those of an Si diode and well satisfy the requirements for t.v. tuners.

Tohru Hara

Papers

GaAs Hall-effect devices fabricated by ion-implantation technique

GaAs varactor diode for u.h.f. t.v. tuners