Tunable High Quality-Factor Silicon Microring Resonator Driven by High-Mobility Transparent Conductive Oxide

We demonstrated a silicon microring resonator driven by a titanium-doped indium oxide capacitor with 10 nm hafnium oxide insulator, achieving a high quality-factor of 11,700 with a high electro-optic tunability of 120 pm/V.

1. Introduction

Silicon microring resonator (MRR) plays a pivotal role in integrated photonic circuits as tunable optical filters and optical modulators due to its compact size. However, most active Si MRRs are driven by reversed PN junctions, which only provide a low electro-optic (E-O) tunability of 40 pm/V [1]. To address this challenge, MRRs with a heterogeneously integrated III-V compound metal-oxide-semiconductor (MOS) capacitor on Si waveguide presented a higher tunability of 55 pm/V [2]. Recently, our group demonstrated an indium-tin-oxide (ITO)-gated Si MRR, which achieved an ultra-high tunability of 271 pm/V using a narrow microring waveguide with a hafnium oxide (HfO₂) insulator [3] along with nanocavity [4] and electro-absorption modulators [5]. However, the quality factor (Q-factor) is limited to 1,000 due to the high optical loss from the ITO gate. To improve the Q-factor of the tunable MRR, high-mobility transparent conductive oxide (TCO) materials are essential to lower the optical loss from the gate as they can reduce the free carrier optical absorption [6]. Titanium-doped indium oxide (ITiO) is one of the high mobility TCO materials and it can achieve 105cm²V^-1s^-1 mobility by a simple RF sputtering process [7]. In this paper, we demonstrated a tunable Si MRR with a heterogeneously integrated ITiO/HfO₂/Si MOS capacitor, which has a high Q-factor of 11,700 with high tunability of 120pm/V. A higher Q-factor of 22,000 is feasible by our further analysis.