Ferroelectric Slot Waveguide Phase Shifter for FEOL Integration
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Solution Overview
Problem
Silicon-based electro-optical (EO) phase shifters suffer from inefficient linear electro-optical effects due to their crystalline structure, and current integration strategies require a wafer bonding process, limiting their integration in electronic-photonic integrated circuits (EPICs) to the back-end of line (BEOL), which results in optical coupling losses.
Innovation Solution
A method is developed to produce an EO phase shifter using a slot waveguide configuration with a conducting bottom layer, a ferroelectric center layer, and a conducting top layer, where the center layer is sandwiched between the bottom and top layers, allowing for a vertical electrical field to enhance the linear electro-optical effect, and integrating the EO phase shifter into the front-end of line (FEOL) of an EPIC, utilizing a SiGe-(Bi)CMOS platform.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If silicon-based EO phase shifters are used, then the device can be fabricated with well-established semiconductor methods, but the linear electro-optical effect efficiency is poor due to zero Pockels effect in crystalline silicon
Solution Approach 1:
The patent employs a composite structure combining crystalline silicon waveguide layers with amorphous silicon EO layers. The crystalline silicon provides excellent fabrication compatibility and optical waveguide properties, while the amorphous silicon layer introduces strong Pockels effect for efficient electro-optical modulation. This composite approach resolves the contradiction by integrating materials with complementary strengths.
2Adaptability or versatility
If wafer bonding process is used for integration, then the EO phase shifter can be integrated into existing platforms, but the integration is limited to back-end of line (BEOL) resulting in optical coupling losses
Solution Approach 1:
The patent transitions from horizontal/planar integration architecture to vertical/three-dimensional integration. By stacking the EO phase shifter directly onto the photonic circuit in the vertical dimension, the design eliminates the need for lateral optical coupling and subsequent re-coupling operations. This vertical integration approach enables FEOL incorporation while eliminating optical coupling losses.
3Use of energy by moving object
If vertical electrical field configuration is used, then the distance between electrodes is reduced improving EO effect, but the device structure becomes more complex
Solution Approach 1:
The vertical electrode layers serve multiple functions simultaneously: they generate the strong vertical electrical field for efficient Pockels effect, they act as electrical connectors between different integration layers, and they provide a scalable template for multi-layer integration. This multi-functionality reduces overall device complexity despite the vertical configuration.
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
This configuration improves the linear electro-optical effect efficiency, reduces energy consumption, and avoids optical coupling losses by integrating the EO phase shifter in the FEOL, enabling monolithically integrated and scalable EO modulators with enhanced performance.
Implementation Method 1
a major issue of known silicon (Si) EO phase shifters is that Si as a material lacks efficient EO effects due to its crystalline structure, where the linear electro-optical effect (LEOE), also known as Pockels effect, is zero in the dipole approximation
Data Source
AI summary
The present invention relates to producing an electro-optical phase shifter such that it may be integrated into a front-end of line of an electronic-photonic integrated circuit. A conducting bottom layer with a first refractive index is provided. A center layer including a ferroelectric material and with a second refractive index is provided on top of a first region of the conducting bottom layer, such that the center layer is not on top of a second region of the conducting bottom layer. A conducting top layer with a third refractive index is provided on top of the center layer. The second refractive index is lower than the first refractive index and lower than the third refractive index, such that the conducting bottom layer, the center layer, and the conducting top layer form a slot waveguide. A first electrical connector which connects the second region of the conducting bottom layer with an upper layer is provided. Additionally, a second electrical connector which connects the conducting top layer with the upper layer is provided. A first electrode and a second electrode are provided in the upper layer such that the first electrode connects to the second region of the conducting bottom layer via the first electrical connector and the second electrode connects to the conducting top layer via the second electrical connector.