Laser tests of the DEPFET gated operation

Abstract

DEPFET is an active pixel particle detector, in which a MOSFET is integrated in each pixel, providing first amplification stage of readout electronics. Excellent signal over noise performance is provided this way. The DEPFET sensor is planned to be used as an inner pixel detector in the BELLE II experiment at electron-positron SuperKEKB collider in Japan. Gated operation of the DEPFET sensor is a unique function which allows making sensor insensitive for incoming radiation for defined time interval. Charge previously integrated in the DEPFET's internal gate is saved and integration can continue afterwards. The insensitive mode of the DEPFET is achieved by a suppressed clear mechanism, which clears newly generated charge in the detector bulk, but keeps charge previously stored in the internal gate by a capacitive coupling to the external gate electrode. The properties of the gated operation were evaluated with the laser beam. It was proven, that DEPFET can operate this way. The average charge selection in the insensitive mode is lower than 0.4% and the suppressed clear mechanism does not cause charge loss higher than 200 electrons. Such fast mechanism which can define a time window, where detector stops integration of new charge, can be used for example to select out noisy bunches injected in an accelerator.