a New Integrated Pixel Detector for High Energy Physics
Several types of radiation such as x-rays, infrared light, and ionizing particles can be detected by means of reverse biased pin-diodes. In high energy physics, pin-diode-based detectors for high energy sub-atomic particles have provided improved signal to noise ratio and better spatial resolution compared to the traditional gas-based detectors, and have become a crucial part in current experiments. We have fabricated integrated pixel devices which have the high-resistivity, signal-charge collecting volume and the readout circuitry in a single piece of silicon. The integration of both detecting elements and circuitry is carried out by building the circuitry on top of the detecting elements maximizing spatial resolution. Signal charge is collected by a designated collection electrode rather than by the circuitry, where it would be lost for readout. The prototype contains an array of 10 by 30 pixels, each 125 by 34 square microns. The manufacturing process, based on the Stanford BiCMOS process, only contains steps used in conventional IC-processing, except for the double-sided processing. Thirteen masks were needed on the front side of the wafer and three on the back to implement both CMOS readout circuitry and detecting elements. A special gettering step helped obtain low leakage currents (the bulk minority carrier lifetime was about 500 microseconds) despite the very high temperature anneals (the well drive-in was 16 hours at 1150 C). Both circuitry and detecting elements are fully functional. Tests with infrared illumination, gamma irradiation and minimum ionizing particles indicated an excellent signal to single-channel noise performance of about 150 to 1 for a minimum ionizing particle, which is an order of magnitude better than silicon strip detectors currently used, a record -breaking position resolution in the direction of smallest pixel (sigma of about 2.2 micron) and good resolution in the other direction. In an efficiency test the detectors did not miss any of the 2665 minimum ionizing particle hits.
- Pub Date:
- PIXEL DETECTOR;
- Engineering: Electronics and Electrical; Physics: Elementary Particles and High Energy