An ultra-low noise Switched Capacitor Transimpedance Amplifier for parallel Scanning Tunneling Microscopy

In this article, we report a custom dual probe Scanning Tunneling Microscopy (STM) system demonstrating simultaneous multi-channel imaging to enhance the imaging throughput of a STM. The dual probe array is fabricated using CMOS-MEMS technology, with each probe having its own fine Z actuator and current sensing amplifier integrated with it to enable independent operation and scaling to large arrays of parallel probes. A novel CMOS Switched-Capacitor Transimpedance Amplifier (SCTIA) is demonstrated to locally sense the tunneling current flowing through the CMOS probe. The SCTIA is sampled at 166 kHz to produce an effective transimpedance gain of 88 MΩ with a tunnel current bandwidth of 40 kHz. Correlated Double Sampling (CDS) is utilized to achieve an input referred noise floor of 25 fA/√Hz.