I. Introduction
THE controlled-drift detector (CDD) was proposed in 1997 [1], and the first experimental evidence of its working principle was reported in [2]. The device is built on a fully depleted 300- m-thick high-resistivity wafer and is operated in integrate-readout mode. The basic idea of the CDD is to generate columns of equally spaced potential wells for the electrons by superposing a periodic perturbation of sufficient amplitude to a linear drift potential. During the integration mode, the signal electrons are stored within these wells. The removal of these potential barriers in an externally controlled way allows the use of the linear drift potential to sweep the electrons toward the readout electrodes. The time between the removal of the barriers and the arrival of the signal electrons at the readout electrodes gives the position of the irradiated pixel along the drift direction. The second coordinate is obtained by providing a separate readout electrode for each pixel column. Arrays of deep -implants provide lateral confinement. In Fig. 1, the layout of the anode region of the controlled-drift detector is shown.