The demand for high-bandwidth interconnects in applications such as data centers and high-performance computing has led to the widespread adoption of optical interconnect solutions. To further enhance the market acceptance of these applications, cost reduction is essential. For this, we realized an avalanche photodetector (APD) that relies on the vertical N+/P-well Si junction for photodetection. It achieves the responsivity of 0.28 A/W and the bandwidth of 5.9 GHz for 0 dBm incident optical power. We implemented a monolithically integrated optical receiver that contains APD, under-damped trans-impedance amplifier, and output buffers using 28-nm standard CMOS technology without any process modification and design rule violation. The fabricated optical receiver successfully operates up to 20 Gb/s. Details of the monolithic optical receiver performance as well as the limiting factors that need to be overcome for further performance improvement will be discussed in the presentation.
Single-photon avalanche diode (SPAD) based sensors and systems enable a variety of applications in biomedical, automotive, consumer, and security domains. While several established standard technologies, which can facilitate the design of SPAD-based systems are already in existence, challenges remain for the development of deep sub-micron monolithic integration of circuits and SPADs. In this work, we present SPADs along with pixel circuits in a standard GF 55 nm BCDL process. Two different designs demonstrate the flexibility allowed by the technology for a variety of applications. Both shallow and deep junction SPADs present excellent noise performance of less than 1 cps/μm2 at 3 V excess bias. An integrated passive-quench active-recharge (PQAR) circuit is used in conjunction with the SPADs, which enables a dead time of less than 2 ns, easily allowing for high dynamic range applications that require < 100 Mcps such as quantum communication and information technologies. The deep and shallow junction SPADs demonstrate an afterpulsing probability of < 0.5 % and < 2 % at 3V excess bias, respectively. The dead time is adjustable through analog control of the active-recharge circuit, allowing for afterpulsing reduction to below 0.1 % while maintaining Mcps operation. The shallow junction, which has a breakdown voltage of about 18 V and a peak sensitivity at 430 nm is particularly interesting for applications requiring low supply voltage, whereas the deep SPAD, which demonstrates < 4 % photon detection probability (PDP) at 940 nm, can be implemented in LiDAR sensors that require enhanced sensitivity at near-infrared (NIR) wavelengths. The measured timing jitter of both SPADs is < 50 ps FWHM at 3 V excess bias and 780 nm.
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