A speed-optimized, low-noise APD with 0.18 μm CMOS technology for the VLC applications

Abstract

A new avalanche photodiode device applied to a visible light communication (VLC) system is designed using a standard 0.18 [Formula: see text]m complementary metal oxide semiconductor process. Compared to regular CMOS APD devices, the proposed device adds a [Formula: see text]-well layer above the deep [Formula: see text]-well/[Formula: see text]-substrate structure, and an [Formula: see text]/[Formula: see text] layer is deposited upon it. The [Formula: see text]/[Formula: see text] layer acts as an avalanche breakdown layer of the device, and an STI structure is used to prevent the edge break prematurely. The simulation results shows that the avalanche breakdown voltage is as low as 9.9 V, dark current is below [Formula: see text] A under −9.5 V bias voltage, and the 3 dB bandwidth is of 5.9 GHz. It is due to the use of the 0.18 [Formula: see text]m CMOS process-specific STI protection ring and short-circuits the connection of the deep [Formula: see text]-well/[Formula: see text]-substrate, and the dark current is reduced to be lower than two orders of magnitude compared to regular CMOS APD. Gain and noise characteristics are accurately calculated from Hayat dead-space model applied to this CMOS APD. So, this device’s gain and excess noise factor are 20 and 2.5, respectively.