تجزیه و تحلیل حساسیت سنسورهای میدان مغناطیسی با استفاده از نوترکیبی وابسته به اسپین در دیودهای سیلیکون

An analysis of the magnetic field sensitivity that could be achieved in a sensor utilizing spin-dependent recombination (SDR) in silicon diodes is presented. Based on current theories of spin-dependent recombination and shot noise in diodes it is predicted that conventional silicon diodes may be used as detectors in a resonant magnetic field sensors with better than 3 μT resolution in a 1 Hz bandwidth – adequate for applications such as compassing, current sensing, position sensors and non-contact switches. A semiconductor device optimized for maximum SDR response will theoretically achieve a resolution on the order of 1 nT.

Spin-dependent recombination (SDR) is an effect in which the recombination rate of electrons and holes in semiconductors depends on the spin polarization of the carriers. This spin polarization can be changed by exciting the system with ac electromagnetic fields at the electron spin resonance (ESR) frequency, corresponding to the energy difference between spin up and spin down states in a dc magnetic field, Bdc. Detecting ESR through the resulting changes in the recombination rate is known in the literature as electrically detected magnetic resonance (EDMR). The schematic in Fig. 1 illustrates the frequency–field relationship for electron spin resonance: the resonance frequency, fESR, is proportional to the energy difference, ΔE, between the spin up and spin down states. ΔE in turn is proportional to the magnitude of the dc magnetic field, Bdc. As a result, the ESR frequency is directly proportional to the dc magnetic field. I.e., fESR = γBdc where γ is the gyromagnetic ratio of the electrons. Of key importance is that γ is temperature-insensitive, allowing for the possibility of realizing an accurate, calibration-free magnetometer or magnetic field sensing technology in silicon. Surprisingly, although EDMR has been widely used to characterize defects in silicon crystals and devices, it has never been exploited directly for any technological application. Full-size image (7 K) Fig. 1. Energy level for an electron in a magnetic field. The energy difference between spin up and spin down is proportional to the magnetic field. Figure options The change in recombination rate that results from the reorientation of spins at ESR is manifest in changes in the current–voltage characteristics of semiconductor devices such as diodes and transistors. Thus, it becomes possible to devise an electronic circuit that measures the magnitude of the dc field by determining the frequency at which a maximum change in device characteristics is detected. Such a resonant magnetometer could then be readily implemented as a standard-cell design in commercial silicon integrated circuit technology, requiring no specialty processing or materials.

We have shown that the magnetic field resolution of a SDR magnetometer using a conventional silicon diode used as a detector will theoretically reach 3 μT/Hz1/2 under optimal bias conditions. Once the optimum electrical bias point has been set, improvements in sensitivity will have to come from changes in device structure or doping. Increasing the diode junction area, A, will increase the device current and reduce the shot noise without affecting the sensitivity. The resulting improvement in resolution will come at the expense of area and power consumption. Since the theoretical maximum ΔR/R is 0.1 compared to 10−4 seen in the experimental devices, several orders of magnitude improvement in sensitivity may be possible using different materials, or by introducing more SDR-efficient recombination centers in Si. Such materials optimization remains to be explored. With current Si devices, the projected resolution is sufficient for many applications such as compassing, current sensing and non-contact position sensing. Since the magnetometer would be implemented entirely in CMOS technology, such functions could easily be added to any integrated circuit.