GaN Stack Acoustic Reflector for High Q Factor Wireless Filters
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Solution Overview
Problem
Current semiconductor technologies face challenges in forming integrated acoustic filters with high quality (Q) and electromechanical coupling coefficient (k2eff) using gallium nitride (GaN) channels, particularly in wireless communication systems, due to poor crystal quality and multi-chip requirements.
Innovation Solution
A method is developed to form a thin-film piezoelectric acoustic filter and a monolithically integrated GaN high-electron-mobility transistor power amplifier (HEMT PA) and CMOS device over a silicon on insulator (SOI) wafer with a GaN-channel/buffer Bragg reflector, utilizing a SOI wafer with a [111] crystal orientation Si handle wafer, buried oxide layer, and alternating layers of high/low acoustic impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If known acoustic filters using layers of GaN are formed, then the device can be manufactured, but the quality factor (Q) and electromechanical coupling coefficient (k2eff) are poor
Solution Approach 1:
The patent changes the crystal orientation parameter from conventional <100> or <110> to <111> orientation for the Si handle wafer. This parameter change in the substrate crystal structure enables the formation of GaN layers with superior piezoelectric properties and crystal quality, directly improving Q and k2eff values while maintaining manufacturability
Solution Approach 2:
The patent employs a composite structure combining Si <111> handle wafer, buried oxide layer, and epitaxially grown GaN layers with specific crystal orientations. This composite material system leverages the advantageous properties of each layer - the Si <111> substrate provides mechanical stability and piezoelectric enhancement, while the GaN layers provide acoustic wave propagation - to achieve high Q and k2eff
2Adaptability or versatility
If multi-chip solutions are used for wireless communication systems, then various components (PA, LNA, switch, filters) can be implemented, but the device complexity and integration are increased
Solution Approach 1:
The patent merges multiple discrete chip functions (power amplifier, low-noise amplifier, switch, and acoustic filters) into a single monolithically integrated device structure. By combining these components on one wafer using the same fabrication process, the patent eliminates the need for multi-chip assemblies, reducing overall device complexity while maintaining full functionality
Solution Approach 2:
The patent creates a universal platform structure based on Si <111> handle wafer with epitaxially grown GaN layers that can simultaneously support multiple functions - acoustic wave propagation for filters, high-electron-mobility transistor formation for PAs and LNAs, and switching functions. This multi-functional platform allows all components to be fabricated using the same process steps, achieving versatility without complexity
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 approach enhances the Q factor and k2eff of the acoustic filter, improving the performance of GaN-based devices for wireless communication systems by integrating a GaN HEMT PA and CMOS with a thin-film acoustic filter and Bragg reflector, suitable for various industrial applications.
Implementation Method 1
forming a Bragg reflector over the crystal orientation Si handle wafer, the Bragg reflector including a GaN stack with alternating layers of high/low acoustic impedance
Implementation Method 2
forming a thin-film piezoelectric acoustic filter
Data Source
AI summary
Methods of forming a thin-film piezoelectric acoustic filter, a GaN-channel/buffer Bragg reflector, and a monolithically integrated GaN HEMT PA and CMOS over a [111] crystal orientation Si handle of a SOI wafer and resulting devices are provided. Embodiments include providing a SOI wafer including a [111] crystal orientation Si handle, a BOX layer, and a top Si layer; forming a CMOS device over the top Si layer; and forming a Bragg reflector over the [111] crystal orientation Si handle wafer, the Bragg reflector including a GaN stack with alternating layers of high/low acoustic impedance.