Conductive-Oxide MOSCAP Microring Modulator for Sub-Volt CMOS Driving
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Solution Overview
Problem
Existing silicon microring modulators (Si-MRMs) require high driving voltages (Vpp) for efficient operation, making them unsuitable for direct driving by CMOS logic circuits and leading to high power consumption in CMOS transmitter circuits.
Innovation Solution
A metal-oxide-semiconductor capacitor (MOSCAP) modulator integrating silicon photonics with transparent conducting oxide (TCO) and a high dielectric constant insulator, featuring a high carrier mobility TCO layer to achieve sub-volt Vpp operation with improved electro-optic modulation efficiency and reduced power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If existing Si-MRMs based on reversed PN junctions are used, then ultra-high modulation bandwidth is achieved, but driving voltage requirement exceeds 2 V making CMOS direct driving infeasible
Solution Approach 1:
The patent changes the electrical parameters of the modulator by replacing the PN junction structure with a MOSCAP structure having a high-k dielectric layer and transparent conducting oxide gate. This structural parameter change enables the modulator to achieve ultra-low Vπ·L values (e.g., 0.12 V·cm) while maintaining high modulation bandwidth, making it compatible with CMOS logic voltage levels.
Solution Approach 2:
The patent employs composite material structures including high-k dielectric materials (e.g., HfO2 with κ≥10) combined with transparent conducting oxides (e.g., ITO, IZO, In2O3:Sn) to create the MOSCAP modulator. This composite structure achieves both low driving voltage and high-speed performance, resolving the contradiction between bandwidth and voltage compatibility.
2Ease of operation
If high voltage-swing CMOS transmitter circuits are used to drive Si-MRMs, then modulation function is achieved, but power consumption increases to hundreds of milliwatts
Solution Approach 1:
By changing the modulator structure to MOSCAP with high-k dielectric and TCO gate, the patent reduces the required driving voltage from >2V to sub-volt levels. This parameter change enables direct CMOS logic driving without high voltage-swing circuits, reducing transmitter power consumption from hundreds of milliwatts to negligible levels since the modulator itself consumes less than 100 fJ/bit energy.
3Use of energy by stationary object
If driving voltage is reduced to enable CMOS direct driving, then power consumption decreases, but modulation efficiency and bandwidth may be compromised
Solution Approach 1:
The patent uses composite materials (high-k dielectric + TCO) to create a MOSCAP structure that achieves ultra-low Vπ·L values while maintaining high-speed performance. The high-k dielectric provides strong electric field confinement for efficient modulation, while the TCO gate enables low-voltage operation with high carrier mobility, preserving bandwidth even at sub-volt driving conditions.
Solution Approach 2:
The patent applies local quality enhancement by using a narrow microring waveguide width (e.g., 300 nm) in the active modulation region to maximize the overlapping factor between accumulated carriers and optical mode profile. This localized optimization achieves high modulation efficiency and bandwidth without requiring high driving voltage.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The MOSCAP Si-MRM achieves efficient electro-optic modulation with a low Vπ·L, enabling high-speed operation at sub-volt Vpp with reduced energy consumption, supporting large photon lifetime-limited bandwidth and balanced Q-factor.
Implementation Method 1
The combination exhibits a high electro-optic modulation efficiency, a low Vπ·L
Implementation Method 2
metal-oxide-semiconductor capacitor (MOSCAP) modulator
Implementation Method 3
a high carrier mobility transparent conducting oxide (HMTCO) deposited on the insulator to form an array, gated by the TCO
Implementation Method 4
nano-sized silicon waveguide
Implementation Method 5
optical microring resonators have emerged as a key building block of photonic integrated circuits
Data Source
AI summary
The disclosure provides a highly efficient MOSCAP modulator that combines silicon photonics with transparent conducting oxide with on-chip wavelength division multiplexing capability. In at least one embodiment, a MOSCAP silicon microring modulator (Si-MRM) is heterogeneously integrated with a nano-sized silicon waveguide, a high dielectric constant insulator deposited on the silicon waveguide, and a high carrier mobility transparent conducting oxide (HMTCO) deposited on the insulator to form an array, gated by the HMTCO. The combination exhibits a high electro-optic modulation efficiency, a low Vπ·L, and consequently can be driven by a sub-volt Vpp at high modulation bandwidth. The utilization of HMTCO reduces the optical waveguide absorption, enabling a balanced Q-factor for sub-volt Vpp modulation while still supporting a large photon lifetime-limited bandwidth. Additionally, the HMTCO, along with optimized doping on the Si microring waveguide and metal electrode patterning, improves the RC bandwidth significantly compared with prior known efforts.