First results from the HEPAPS4 active pixel sensor

Active pixel sensors are monolithic solid state devices based on CMOS technology with the sensing element and front-end electronics integrated in the same substrate. The HEPAPS4 active pixel sensor is designed specifically for charged particle detection with future e + e - colliders as one possible application in high energy physics. The sensor has an array of 1024×384 pixels of size 15 × 15 μ m 2 , with the conventional design of three NMOS transistors implemented in the 20 μ m epi-layer. The signal of each pixel is multiplexed out on four ports and sampled by an off-chip ADC. The readout system developed for the chip features different reset modes, variable readout region and integration time, with the possibility of external triggering. This paper reports on the first characterisation of this device, using photonic methods to measure gain, linearity, dynamic range and dark current.