Fully Integrated Electronic-Photonic Ultrasound Receiver Array for Endoscopic Applications in a Zero-Change 45-nm CMOS-SOI Process

This article presents the first fully integrated 2-D array of electronic-photonic ultrasound sensors targeting low-power miniaturized ultrasound probes for endoscopic applications. Fabricated in a zero-change 45-nm CMOSsilicon-on-insulator (SOI) technology, this 5.53 x 3.03 mm electronic-photonic system on chip (EPSoC) utilizes micro-ring resonators (MRRs) as ultrasound sensors instead of the traditional piezoelectric or capacitive micromachined transducers (PMUTs or CMUTs). The photonic nature of the sensor enables remoting of the power-hungry receive electronics outside the probe tip, thus lowering the power dissipation inside the human body. Moreover, it eliminates electrical cabling, replacing the bulky micro-coax cables with thinner optic fibers. This EPSoC also reduces fiber count by 8x with zero power and area overhead by performing wavelength division multiplexed interrogation of MRR sensors coupled onto the same waveguide in lieu of sub-array beamforming or in-pixel digitization. Leveraging the monolithic integration of photonic devices with CMOS circuitry, a complete receiver (RX) unit is built right next to the sensor MRRs, including a programmable gain transimpedance amplifier (TIA) and background current cancellation digital-to analog converters (IDACs), which allow for a sensor operating range of 74 dB. A 9-bit SAR ADC performs on-chip A/D conversion making for a self-contained endoscopic ultrasound receiver system. The photonic sensing element demonstrates 7.3 mV/kPa sensitivity while consuming 0.43 mW of power and occupying 0.01 mm of area. The functionality of the fabricated chip has been demonstrated in ultrasonic receiver beamforming experiments.