Abstract
In this paper, we present a systematic design for manufacturing analysis for thermo-optic phase tuners, framed within the process modules available on a silicon nitride platform. Departing from an established technology platform, the heat distribution in various micro-structures was analyzed, both in steady and transient states, employing a 2D heat transfer model solved numerically. Multi-parametric simulations were performed on designs combining trenches and substrate undercut, by varying their position and dimensions. The simulation results were compared to a reference conventional fully-clad cross-section. Deep air-filled trenches are shown to reduce the power consumption up to 70%, alongside a thermal crosstalk phase shift reduction of more than one order of magnitude (0.045 π rad/mm), at the expense of a slightly lower bandwidth (11.8 kHz). The design with trenches and substrate undercut lowers the power consumption up to 97%, decreases two orders of magnitude the crosstalk (0.006 π rad/mm), at the cost of less than one order of magnitude in bandwidth (0.9 kHz). In the works, we selected three different heater materials (Cr/Au, Al, poly-silicon) offered by the fab and four different heater widths (2.5 to 7 μm). Their combinations are related to performance, reliability and durability of the devices, strongly linked to temperature, current density, and Omegaic resistance. The different figures of merit defined, and the methodology followed, can be mimicked by future designers to take design decisions at bird’s eye.
Highlights
The high demand for discrete optical devices in many applications over the four last decades, fostered a rapid evolution and cost reduction in the photonics subsystems.With photonics becoming ubiquitous in many application domains, there is a general demand for the reduction in space, weight, and power (SWaP) consumption
The three main established photonic technologies [3,4,5,6] are based on Silicon (Si), Indium Phosphide (InP) [7,8,9], and Silicon Nitride (SiN) [10,11,12] with differentiated performances depending on the device function: III–V semiconductors for light generation, amplification and modulation, Si
We show a design for manufacturability flow addressing the thermal wanted and unwanted effects, by analyzing how the dimensions and position of known micro-structures, such as trenches and undercuts, besides the heater material, are related to the performance parameters: power consumption, cross-talk, and bandwidth
Summary
The high demand for discrete optical devices in many applications over the four last decades, fostered a rapid evolution and cost reduction in the photonics subsystems. Runs [1,2] allowed a step forward on photonic integrated circuits (PICs) technologies, due to the development of new fabrication processes for different technology platforms. These have paved the way for an effective integration, reducing manufacturing costs, and SWaP requirements while increasing performance and stability. Power consumption and thermal crosstalk are the main drawbacks of integrated TO phase shifters, but resorting to some additional fab steps, techniques, or structures in order to overcome them have been demonstrated, including: the thermal isolation of the TO phase shifter by means of trenches and undercuts [28,29,30,31,32], the heat flux transfer increase towards the shifter’s waveguide by inserting high thermal conductivity materials [33] or dopants at specific locations of the shifter [32]. A discussion on durability and the inter-relation of all the figures of merit (FoM), including footprint, closes the paper
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