This thesis describes an integrated silicon vertical geometry carrier-domain magnetometer fabricated on a silicon substrate using a commercial linear bipolar process. It also describes several chips in which CDMs are used in conjunction with other circuit elements to implement a integrated magnetometer subsystem and other applications that use VCDMs.
CDMs are inherently regenerative npnp structures in which conduction is lirnited to a small region of the device (domain). During operation two such domains ,one for holes and another for electrons exist. The two domains interact with each other reinforcing any effect (e.g. magnetic steering) that results in a perturbation of the path followed by the carriers that constitute these domains. The positive regeneration enhances the sensitivity of the device, allowing the detection of very small fields (on the order of 50 mG.).
The CDM geometry has been designed to minimize signal offsets by minimizing asymmetries due to alignment errors during the fabrication. Vertical geometry (instead of lateral) was used to permit its fabrication using a standard bipolar process and to increase the current capacity to produce an improved absolute sensitivity. A new way to increase the regeneration of the device further and, therefore, to increase its sensitivity is also described. The present sensitivity is in fact the largest reported for silicon magnetic sensors (0.72pAl G at 7mA drive current).
An integrated flat coil that enables us to produce a local magnetic field was integrated with the CDM. The coil has been used not only to test the devices on the wafer but also to provide a magnetic field reference to autocalibrate the sensitivity of the magnetometer and therefore eliminate the influence of environmental variables such as temperature.
The CDMs were integrated with the corresponding amplifying and signal conditioning circuitry to obtain subassemblies that produce analog (voltage or current) or frequency modulated outputs.
A magnetic coupler in which the coil and the VCDM are used to communicate signals between two dielectrically isolated circuits was also fabricated. Two VCDMs were used for this application to cancel the effects of magnetic fields from sources other than the coil to achieve immunity to externally applied fields.
An array of four VCDMs sharing a common amplifier was also implemented. The devices can be selectively turned on and off by digital signals allowing the mapping of the magnetic field over the area of a chip.
December 31, 1986
Goicolea, J. I. (1986). Design, Theory, and Applications of Integrable Carrier-domain Magnetometers. United States: University of California, Berkeley.