Semiconductor MRs and Hall-effect devices are commonly used in the automotive industry for sensing the position of engine crankshafts and camshafts. FIG. 1 schematically depicts the layered structure of a typical semiconductor MR 10 comprising an epitaxial thin film of indium antimonide (InSb) 12 grown or otherwise deposited on a gallium arsenide (GaAs) substrate 14 and which is doped n-type with tellurium (Te) 16 during growth of the film. Other aspects of the device which are not shown and which are not unique to the present invention typically include: a pattern which is etched in the InSb epitaxial film, metal contacts, dielectric passivation, the device mounted on a permanent magnet or ferromagnetic material, wires which are bonded to the metal contacts, overmolding material, etc. These aspects are well known in the art.
Some of the relevant improvements which have been made in this art include a non-uniform n-type doping profile in the indium antimonide film (Partin et al. U.S. Pat. No. 5,184,106), a layer of indium antimonide which is heavily doped n-type near the surface to facilitate making low resistance electrical contacts (Partin et al. U.S. Pat. No. 5,153,557), adding a buffer layer of high resistivity indium aluminum antimonide between the electrically insulating substrate and the indium antimonide active layer of the device (Partin U.S. Pat. No. 5,883,564), and techniques for using a silicon substrate instead of a gallium arsenide substrate (Partin et al. U.S. Pat. No. 5,491,461). These patents generally disclose that the optimum MR device has a maximum electron mobility and hence a maximum sensitivity to a magnetic field. While these devices may be used singly, pairs of them are sometimes used to measure the differential magnetic field and hence reduce their sensitivity to temperature changes. In another development, an array of MR devices can be used to measure the magnetic field at a distribution of locations (Schroeder U.S. Pat. No. 6,201,466). Such an array can be used for facilitating sensing of the variation of magnetic field caused by a permanent magnet, electromagnet, ferromagnetic object or by eddy currents.
Other conventional semiconductor MR devices use either an InSb film, or an InSb bulk material, having similar, or no dopants. NiSb needle-like inclusions are usually incorporated into the bulk material in order to increase the device sensitivity. Some of these devices are not epitaxial, but are polycrystalline indium antimonide films on a glass or ceramic substrate. These conventional magneto-resistive sensors, which are dependent upon electron mobility, are known to have functional limitations in that they are relatively temperature-dependent, which compromises their sensing performance. FIG. 2 depicts, in graphical form, the relationship between electron mobility and temperature in indium antimonide that is doped n-type, having an average electron density at 300K of approximately 1×1017 cm−3. Further, most conventional InSb magnetic position sensors can only perform digital functions because of their temperature sensitivity. Therefore, there is a need for an improved InSb-based magnetic position sensor having a controlled electron mobility which is substantially temperature-independent and which can also perform both analog and digital functions. The present invention satisfies those needs, as well as others, and overcomes the deficiencies known to exist in currently available MR devices. It is also useful for making Hall-effect devices and arrays of Hall-effect devices that are temperature insensitive.
Prior publications on indium gallium antimonide epitaxial thin films, which were nominally undoped or lightly doped (below about 6×1016 cm−3 electron density), include:                1) J. H. Roslund et al., “Si-doped and Undoped Ga1−xInxSb Grown By Molecular Beam Epitaxy on GaAs Substrates,” J. Appl. Phys., Vol. 80, pp. 6556–58 (1996).        2) W. M. Coderre et al. “Conduction Bands of Ga1−xInxSb,” Can. J. Physics, Vol. 47, pp. 2553–63 (1969).        3) Y. Amemiya, et al., “Electrical Properties of InSb-based Mixed Crystal Films,” J. Appl. Phys. Vol. 44, pp. 1625–30 (1973).        
In these devices, the electron mobilities vary substantially over temperature, typically more than forty percent (40%) over the temperature range from negative forty degrees Celsius to two hundred degrees Celsius (−40° C. to 200° C.).
An alternative technique, which is not part of the current invention for obtaining InSb with a small temperature coefficient of the electron mobility, is to dope with the rare earth elements erbium and samarium, as documented in the following publications:                1) D. L. Partin et al., “Samarium Doping of Molecular Beam Epitaxially Grown InSb on InP,” J. Vac. Sci. Technol. Vol. 10, pp. 873–76 (1992).        2) J. Heremans et al., “Erbium Doping of Molecular Beam Epitaxially Grown InSb on InP,” J. Vac. Sci. Technol., Vol. 10, pp. 659–63 (1992).        
Doping indium antimonide thin films n-type with tellurium is well known in the art, and is described in the following publication:                D. L. Partin et al., “Growth and Characterization of Indium Antimonide Doped With Lead Telluride,” J. Appl. Phys., Vol. 71, pp. 2328–32 (1992).Other relevant patents directed to the state of the art of galvanomagnetic devices include:        
Heremans et al. U.S. Pat. No. 5,314,547 and Kawasaki et al. U.S. Pat. No. 5,385,864.
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