The capacitive coupling between an active sensor and a readout ASIC has been considered in the framework of the CLIC vertex detector study. The CLICpix Capacitively Coupled Pixel Detector (C3PD) is a High-Voltage CMOS sensor chip produced in a commercial 180 nm HV-CMOS process for this purpose. The sensor was designed to be connected to the CLICpix2 readout chip. It therefore matches the dimensions of the readout chip, featuring a matrix of 128 × 128 square pixels with 25 μm pitch. The sensor chip has been produced with the standard value for the substrate resistivity (∼ 20 Ωcm) and it has been characterised in standalone testing mode, before receiving and testing capacitively coupled assemblies. The standalone measurement results show a rise time of ∼ 20 ns for a power consumption of 5 μW/pixel. Production of the C3PD HV-CMOS sensor chip with higher substrate resistivity wafers (∼ 20, 80, 200 and 1000 Ωcm) is foreseen. The expected benefits of the higher substrate resistivity will be studied using future assemblies with the readout chip.
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