A Dual Probe STM Imaging System and a Low Noise Switched-Capacitor Transimpedance Amplifier

This article reports a dual probe STM imaging system that doubles traditional STM frame rate and is capable of being scaled up to perform highly parallel STM imaging. A CMOS MEMS probe array is controlled by two off-chip servo loops to generate two STM images simultaneously. A CMOS switched-capacitor transimpedance amplifier (SCTIA) is integrated with the CMOS MEMS probe to locally sense tunneling current and facilitate future extension to much larger arrays. The SCTIA is sampled at the frequency of 166 kHz to produce an ultra-high transimpedance gain of 88 MQ with a tunnel current bandwidth of 40 kHz. Correlated double sampling is utilized to just 25 fA/√Hz. This novel SCTIA is designed and fabricated achieve an extremely low input referred noise current floor of in a 0.35 μm BiCMOS process, with its core SCTIA occupying an area of just 0.02 mm².