Development of a Monolithic Active Pixel Sensor Using SOI Technology With a Thick Device Layer

Monolithic active pixel detectors fabricated in SOI (silicon on insulator) technology are novel sensors of ionizing radiation which exploit SOI substrates for the integration of readout electronics with a pixel detector. The fully-depleted sensing diode is manufactured under the SOI buried oxide (BOX) in the volume of the `handle wafer', while readout circuitry occupies the upper silicon SOI `device layer'. However, the initial prototypes suffered from significant leakage currents and early breakdown of pixel diodes. These effects limited the production yield. Moreover, the p-wells within the device layer extended to the interface with the BOX, which caused some local potential wells below the BOX at the top of the depleted sensor area. As a result, the effective charge collection efficiency was significantly decreased. This paper describes a solution for these problems employing a thicker 4 ¿m SOI device layer. The use of this detector structure has increased the effective charge collection efficiency to over 99%.