The proposed technology involves the sensitive detection of magnetic fields using the zero-field, spin-dependent recombination (SDR) phenomenon that naturally arises from atomic-scale, deep-level defects intrinsic to silicon carbide (SiC) microelectronics. The SDR phenomenon enables the fabrication of SiC-based magnetic field sensing diodes that are ideal for the development of miniaturized and purely electrical-based magnetometers.

A conceptual illustration of a 3-axis set of Helmholtz coils that houses the SiC diode. Each set of coils is used to provide a modulated magnetic field (each dimension utilizing an orthogonal waveform at audio frequencies) and a low-frequency (<10 Hz) cancellation field to maintain a local region of zero-magnetic field at its interior. As a single electronic device is required for field sensing, the coils can be manufactured on extremely small scales for possible incorporation into a MEMS package.
The magnetometer functions by continually monitoring magnetic field-dependent changes in current measured from a 4H-SiC diode. The instrument uses three orthogonal, single-turn Helmholtz coils for magnetic field modulation and magnetic field cancellation. Each coil modulates the external magnetic field (orthogonal audio waveforms) that frequency division multiplexes the three current components onto a single channel. The diode current is conditioned, digitized, and then fed through three independent digital demodulators to extract the embedded current components. Controllers then track the zero crossings of these components and drive each coil with the required current needed to maintain the region of zero magnetic field across the volume of the diode. As the driving current in these coils is directly proportional to the magnetic field it generates, its measure will serve as an indirect measure of the field being cancelled in each dimension.

The crystalline nature of the 4H-SiC diode allows for a sharp magnetoresponse to be detected at precisely zero Gauss and at symmetrically spaced, electron- nuclear hyperfine interactions. These hyperfine responses may serve to self-calibrate the magnetometer as they are virtually independent of temperature and tremendously stable over long periods of time. The sharpness and high SNR of the magneto-response will allow for sensitivities below 100 pT/Hz½ to be achieved, making the technology competitive with the fluxgate and optically pumped He heritage designs. However, the SiC magnetometer’s purely electrical design is simpler to implement as it does not require inductive sensing elements, high-frequency radio, or optical circuitry that requires stable temperatures for operation. As only a single diode (sensing area 2) is required for simultaneous measurement of three magnetic axes, the technology can be made significantly more compact and lightweight than heritage instruments. Thus, the technology is well suited for swarms of picosats capable of science returns not possible with a single large-scale satellite. Additionally, the 3.3eV bandgap of 4H-SiC makes the material inherently rad-hard and allows for operation in temperatures of over 500 °C. This robustness allows for operation in the harsh environments of the Venusian surface and radiation belts of Jupiter.

This work was done by Corey J. Cochrane of Caltech for NASA’s Jet Propulsion Laboratory. NASA is actively seeking licensees to commercialize this technology. Please contact Dan Broderick at This email address is being protected from spambots. You need JavaScript enabled to view it. to initiate licensing discussions. NPO-49854

NASA Tech Briefs Magazine

This article first appeared in the May, 2016 issue of NASA Tech Briefs Magazine.

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