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The crystallization of complex oxide thin films on amorphous substrates presents a significant challenge because of the lack of long-range order in these substrates and the subsequent difficulty in controlling crystal growth. Nanocrystals with similar crystal structure have the potential to serve as nucleation sites for crystallization and can facilitate this integration. Isolated nanocrystals of strontium titanate (SrTiO3) can be produced on amorphous SiO2 surfaces through crystallization and ripening of initially amorphous layers of SrTiO3. The resulting SrTiO3 nanocrystals exhibit characteristic lateral radii ranging from tens to hundreds of nm and a consistent average height of 1–2 nm across this range. The area density and mean radii of the nanocrystals can be selected by adjusting the deposition and heating parameters, including the amount of deposited SrTiO3 and the heating duration. The heating-time dependence of the area density and mean radii of the nanocrystals is consistent with predictions based on Ostwald ripening kinetics. The selection of these parameters facilitates the use of SrTiO3 nanocrystals as nucleation sites to crystallize the subsequently deposited layer. 

Growing interconnect bandwidth demand in large datacenters requires energy-efficient optical transceivers that operate with four-level pulse amplitude modulation (PAM4) to enable high per-wavelength data rates. Further increases in bandwidth density is possible by leveraging wavelength-division multiplexing (WDM), which optical link architectures based on silicon photonic microring modulators (MRMs) and drop filters inherently enable. This paper presents high-speed PAM4 transmitter and receiver front-ends implemented in a 28nm CMOS process that are co-designed with these silicon photonic optical devices to enable energy-efficient operation. The transmitter utilizes an optical digital-to-analog converter (DAC) approach with two PAM2 AC-coupled pulsed-cascode high-swing voltage-mode output stages to drive the MRM MSB/LSB segments. A 3.42Vppd output swing is achieved when operating at 80Gb/s PAM4 with an energy efficiency of 3.66pJ/bit. The receiver front-end interfaces with a silicon-germanium avalanche photodiode (APD) and utilizes a low-bandwidth input transimpedance amplifier followed by continuous-time linear equalizer and variable-gain amplifier stages. Biasing the APD to realize a gain of 2 allows for -7dBm optical modulation amplitude (OMA) sensitivity at 56Gb/s PAM4 with a BER=10-4 and an energy efficiency of 1.61pJ/bit. Experimental verification of the full PAM4 transceiver at 50Gb/s operation shows -4.66dBm OMA sensitivity at a BER~4x10-4.