Split-drain MOSFET magnetic sensor arrays*1

James J. Clark

Division of Applied Sciences, Harvard University, Cambridge, MA 02138 U.S.A.

Received 18 October 1988;  revised 21 February 1989;  accepted 27 February 1989.  Available online 29 October 2001.


The design of a monolithic split-drain MAGFET magnetic sensor array, implemented in a standard 3u CMOS process, is detailed.

The MAGFETs in the array are scanned in a raster scan fashion. The rows are scanned by allowing current to flow through all elements in a given row, while all other rows are turned off. We present two different methods for performing the column scanning. In the first method, while a row is selected, the differential current output of the sensing elements in the row is amplified by a current mirror transresistance ampfifier which provides conversion of the current differential to a single ended voltage. The outputs of the current mirrors are then multiplexed to provide the column scan. The multiplexed signal then goes into a buffer stage which provides additional amplification and lowers the output impedance for driving external loads. The second scanning method is similar, but does the column multiplexing before the current mirror amplification stage.

32 × 32 and 64 × 64 element arrays have been implemented in 3u CMOS, through the MOSIS facility. Experimental results on the sensitivity of individual sensing elements as well as magnetic field images produced by these arrays are presented. The problems of sensor-to-sensor non-uniformity and the sensitivity of the arrays to interference from non-magnetic influences, especially the effect of stresses in the silicon substrate of the sensor chip, are discussed.
This paper is an extended version of the paper given at the 1988 IEEE Workshop on Solid State Sensors and Actuators, held at Hilton Head Island, SC, June 6¯9, 1988.