Characterization of the RD50-MPW2 monolithic CMOS sensor with the TPA-TCT technique

We present the analysis of a monolithic pixel particle detector (Depleted Monolithic Active Pixel Sensor, DMAPS) by the Two Photon Absortion Transient Current Technique (TPA-TCT). The TPA-TCT gives 3D sensitivity maps with micrometer resolution, enabling the direct measurement of the depletion depth, the 3D Charge Collection Efficiency (CCE) and the boundaries of the embedded electric field. The chip under test is the MPW2, an 8x8 DMAPS pixel matrix, designed by the CERN RD50 collaboration. The TPA-TCT technique is specially suited for evaluating monolithic pixel detectors as it can reach the sensitive volume of every pixel element in the matrix by illumination from the backside. This is possible as as silicon is transparent for the used near infrared laser light (1550 nm). Its spatial resolution can resolve the boundaries of the detector sensitive volume even for small area pixels (60μmx 60μm in this case). The wrap figure shows the experimental laser setup used for the device characterization described in the main article.