H.P. Baltes

Integrated semiconductor magnetic field sensors

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.

A new approach for the fabrication of micromechanical structures

Abstract Many inherent features available in the CMOS process lend themselves to the fabrication of certain micromechanical structures for sensor applications. These micromechanical structures are fabricated by implementing unconventional layout designs in CMOS technology without altering the process sequence. A single post-processing etching step is introduced to form free-standing microstructures on a CMOS IC without affecting the circuitry formed on the chip, thus allowing micromechanical sensors to be produced with pertinent on-chip circuitry for signal conditioning. Polysilicon micro-bridges, sandwiched oxide microbridges and cantilevers are produced using this technique.

Two-dimensional numerical modeling of magnetic-field sensors in CMOS technology

We present two-dimensional numerical simulations of two types of integrated silicon magnetic-field sensors realized recently in standard CMOS technology, viz. the split-drain MOSFET and the vertical Hall-effect device sensitive to magnetic fields perpendicular and parallel to the chip surface, respectively. Our results include potential, current, and surface charge distributions as well as sensitivity, linearity, and noise. Improved device geometries are suggested. Both the finite-difference method and a novel Greens function approach are used for solving the differential equations governing the carrier transport in the presence of a magnetic field.

A CMOS magnetic field sensor

The authors present a novel, fully integrated magnetic field sensor made in the standard, polysilicon-gate CMOS technology. The circuit shows a sensitivity of 1.2 V/T with 10 V supply voltage and 100 /spl mu/A current consumption. The circuit consists of a pair of split-drain MOS transistors in a CMOS-differential amplifier-like configuration.

Dual-collector magnetotransistor optimized with respect to injection modulation

Abstract A dual-collector version of the lateral bipolar magnetotransistor is presented. The device is designed to enhance the injection modulation mechanism by means of (i) low emitter efficiency and (ii) confinement of base current by a diffusion ring. The theory of injection modulation by a magnetic field is further developed. It turns out that the device is equivalent to a merged version of a Hall plate (base region) with a joint-emitter bipolar transistor pair. For small magnetic fields, the transduction efficiency is proportional to the device current and the magnetic field and inversely proportional to the effective base thickness and the equivalent thermal voltage. Experimental results corroborate the theoretical predictions. In particular, the presence of the diffusion ring enhances the sensitivity at 1 T by a factor 6. The linearity for fields up to 300 G is better than 10 −3 .

Operating principle of dual collector magnetotransistors studied by two-dimensional simulation

Dual collector magnetotransistors are magnetic-field-sensitive devices currently developed in several laboratories. Optimized sensor design is often attempted by trial and error rather than by established design rules. This motivated the present comprehensive study of the operation of magnetotransistors by accurate two-dimensional numerical simulations. We model vertical and lateral transistors as obtained by industrial IC technology on the basis of data provided by the chip manufacturer. We consider the entire device structure with the full, complex device geometry, and the physically proper boundary conditions. Our simulations reveal the details, controversial hitherto, of the operating principle of these devices. In particular we find that, in the case of the vertical transistor, it is essentially the emitter injection modulation effect which dominates the sensor response. In the case of the lateral transistor, the magnetic sensitivity is predominantly determined by minority-carrier deflection, although side effects are involved as well. By variation of the doping profile and the device geometry we derive rules for optimized magnetotransistor design. >

High accuracy modeling of photodiode quantum efficiency

We propose a new silicon photodiode model optimized for high-accuracy measurement usage. The new model differs from previous models in that the contribution to the quantum efficiency from the diode front region is described by an integral transform of the equilibrium minority carrier concentration. This description is accurate as long as the recombination of excess minority carriers in the front region occurs only at the front surface and the diode is operating linearly.

An integrated silicon magnetic field sensor using the magnetodiode principle

We report a novel integrated magnetic field sensitive device. Its structure is reminiscent of the bipolar transistor, but its operation is essentially that of a magnetodiode: a reverse-biased p-n (collector) junction plays a role similar to that of the high recombining surface of classical magnetodiodes. The device can be manufactured in standard bulk CMOS or bipolar technology. Sensitivity up to 25 V/T at 10-mA current is achieved. Voltage-current characteristics shows saturation and negative resistance regions, which are explained by JFET and UJT effects, respectively.

Analytic representation of the silicon absorption coefficient in the indirect transition region

The absorption coefficient of silicon over most of the indirect transi region is calculated by fitting an eleven-parameter equation to observed data, an essential step in modeling silicon solar cells./aip/.

Two-dimensional numerical analysis of a silicon magnetic field sensor

We present two-dimensional numerical solutions of the coupled, nonlinear, partial differential equations governing the electric potential, carrier drift, diffusion, generation, and recombination in a finite semiconductor slab in the presence of a magnetic field. This enables device modeling for general geometries, doping levels, and injection conditions, where the effect of the magnetic field cannot be expressed simply in terms of Hall voltage, Lorentz deflection, or magnetoconcentration.