Mitigation of parasitic junction formation in compact resonant modulators with doped silicon heaters
While the high index contrast between silicon and silicon dioxide in the silicon-on-insulator photonics platform permits unprecedented device density, it also leads to high sensitivity to fabrication variations. In silicon microring and microdisk resonator devices, fabrication variations can substantially change the target resonance wavelength. Silicon's high thermo-optic coefficient allows for correction of these fabrication variations and stabilization of the device resonant wavelength through thermal tuning. Metal and doped silicon integrated heaters are commonly used to perform this tuning and have become an essential feature of silicon microring and microdisk modulators. Metal heaters are typically placed in a layer above the silicon devices, while doped silicon heaters are placed in the same silicon waveguide layer, adjacent to the devices. The advantage of doped silicon heaters over metal heaters is due to proximity of the heater to the optical device, leading to greater efficiencies. However, for active devices using p-n junctions such as modulators, parasitic junctions can form between the doped heater and the modulator junctions, resulting in highly unstable and substandard device performance. Here, we present a detailed simulation framework for heater design in resonant silicon microdisk modulators, supported by experimentally measured device performance, which emphasizes tuning efficiency while eliminating parasitic diode formation. Simulations were conducted in Ansys Lumerical HEAT, CHARGE, and MODE to model parasitic junction behavior between the heater and modulator, in addition to the heater's thermal response and its effect on the resonant wavelength of the microdisk.