Quantum sensing technology has emerged as a promising field with superior sensitivity and accuracy in magnetic field sensing compared to conventional technologies. This breakthrough offers significant prospects in the biomedical sector, particularly in the realm of medical imaging. This project focuses on the implementation of quantum sensing using an array of single Nitrogen Vacancy (NV) centers combined with an array of Single Photon Avalanche Diodes (SPADs). SPADs are available in various technologies and forms. To identify the optimal SPAD for this specific application, different SPADs with diverse parameters are designed on a chip using standard 40 nm TSMC process. These parameters include active area, active area shape and metal shielding. The research aims to validate and characterize the performance of these distinct SPADs. However, during the validation tests, it was observed that the SPADs did not meet the criteria. The presence of ESD diodes on the chip introduced a low resistance current path, thereby hindering the characterisation process of the SPADs. Solutions to fix this problem and improve the system are provided. The documented validation methods include general chip testing, establishing the I-V curves of the SPADs and avalanche and quenching testing. In addition, the characterisation methods for junction capacitance, dark count rate (DCR), photon detection probability (PDP) and time jitter are given. For characterizing DCR and PDP a readout system is designed. It consists of an analog-to-digital converter (ADC), FPGA and Arduino. The data is communicated continuously to a PC. The ADC is not fully tested. On the other hand, the FPGA and Arduino are tested and verified to be sufficient for the DCR measurements. The readout system is too inaccurate for PDP measurements. A recommendation on how to make the readout system sufficient for PDP is given.

In this Bachelor graduation project, a 16x16 Single Photon Avalanche Diode (SPAD) array is designed in 40nm TSMC CMOS for diamond single Nitrogen Vacancy center array readout. It includes an active quenching and recharge circuit (AQC), a hold-off circuit for controllable dead-time and IO electronics for off-chip communication. The chip is part of a proposed high sensitivity magnetometer based on single NV center readout with a focus on detecting cancer in biological samples. From the Quantum Integration Technology (QIT) lab, pre-designed SPADs were received to be implemented into the design together with SPAD quenching, recharge and input-output controller electronics. A SPAD model is adapted from literature for simulations of the electric behaviour of the electronics. We present a design and implementation of the Active Quenching Circuit (AQC), a design and implementation of the recharge and hold-off circuits, Input-Output (IO) interface design and implementation and the final top-level implementation ready for the next tape out. Post-layout simulations show negligible speed slowdown and distortion. The AQC has a 12ns quenching time and a 1ns recharge time, leading to a theoretical maximum count rate of 76Mc/s. The hold-off circuit has a tunable dead-time for afterpulsing reduction and 16, 16 bit parallel-in-serial-out (PISO) modules allow per-row readout of the array. The electronics are co-located with the SPADs and pixel pitch is 24𝜇m. The final chip design meets the single NV fluorescence count rate requirement of above 3 Mc/s, the 1.1x1.1 𝑚𝑚2 area requirement, the 32-pin IO requirement, the 16x16 SPAD pixel requirement and, steps have been taken to ensure acceptable crosstalk levels in the array. Finally, the SPAD array chip is designed to run on a 1GHz clock. It should interface with an FPGA that configures the hold-off circuit and reads out the SPAD status bits.