Wafer-Level Thermal IR Sensor Packaging for Thin High-Resolution Arrays
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Solution Overview
Problem
Current thermal infrared sensor arrays face challenges in achieving high spatial resolving power and minimal housing dimensions, particularly in smartphone applications, due to large pixel sizes and increased mechanical dimensions from additional chopper or shutter modules, which hinder miniaturization and increase signal loss through thermal conduction.
Innovation Solution
A method involving the processing and thinning of multiple semiconductor wafers to create a vacuum-filled wafer-level package with reduced thickness, allowing for smaller thermopile pixels and integrated signal processing, using antireflection layers and filter structures to enhance infrared transmission while maintaining mechanical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional housings (metal TO series) are used for hermetic encapsulation, then sealing reliability is improved, but housing dimensions become too large for smartphone integration
Solution Approach 1:
The housing is divided into a modular wafer-level package structure consisting of a sensor wafer, a carrier wafer, and a lid wafer, each processed separately and then assembled. This segmentation enables miniaturization while maintaining hermetic sealing through precise wafer bonding interfaces.
Solution Approach 2:
The patent replaces conventional mechanical housing structures with a wafer-level packaging approach using silicon-based wafers and wafer bonding technology. This substitution achieves hermetic sealing at the wafer level rather than requiring large external metal housings, enabling integration into smartphone form factors.
2Measurement precision
If additional mechanical choppers or shutters are installed in the beam path to achieve required measurement accuracies, then measurement precision is improved, but device complexity and housing height increase
Solution Approach 1:
The patent extracts and eliminates the need for mechanical choppers and shutters from the optical beam path by using thermopile sensor arrays that inherently provide the required measurement accuracy without moving parts. This extraction simplifies the device structure and reduces housing height.
Solution Approach 2:
The patent replaces mechanical modulation systems (choppers and shutters) with a static thermopile sensor array that achieves measurement accuracy through its sensor design and signal processing, eliminating the need for mechanical moving parts in the optical path.
3Measurement precision
If pixel dimensions are reduced for high spatial resolution, then spatial resolving power is improved, but signal loss through thermal conduction increases
Solution Approach 1:
The patent introduces a vacuum environment as an intermediary between the sensor pixels and the external environment. This vacuum acts as a thermal insulation barrier that reduces thermal conduction losses, enabling smaller pixel dimensions to maintain their signal while achieving high spatial resolution.
Solution Approach 2:
The patent creates an inert vacuum environment within the wafer-level package to eliminate thermal conduction through gas molecules. This inert atmosphere prevents thermal energy loss from the small pixel elements, allowing high spatial resolution without proportionally increased signal loss.
4Volume of moving object
If wafer thinning is performed to reduce housing height, then housing dimensions are improved, but mechanical stability and handling difficulty worsen
Solution Approach 1:
The patent uses composite wafer structures consisting of multiple bonded layers (sensor wafer, carrier wafer, lid wafer) that provide mechanical strength while maintaining thin overall dimensions. The composite structure distributes mechanical stresses across multiple interfaces, enabling thin profiling without sacrificing structural integrity.
Solution Approach 2:
The patent employs a nested wafer structure where the thinned sensor wafer is bonded to a carrier wafer, which in turn is enclosed by a lid wafer. This nested arrangement provides mechanical support and protection to the thin central wafer, enabling reduced housing height while maintaining handling stability.
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 enables the production of high-resolution thermal infrared sensor arrays with very small pixels and minimal housing dimensions, improving spatial resolving power and reducing signal loss through efficient thermal insulation and integrated signal processing, suitable for compact mobile devices like smartphones.
Implementation Method 1
a cavity (11) respectively being located over each sensor pixel (5) in the sensor wafer (3) for thermal insulation of the sensor pixels (5) from the substrate
Implementation Method 2
both wafer sides are subsequently provided with antireflection layers (2)
Data Source
AI summary
A method for producing a thermal infrared sensor array in a vacuum-filled wafer-level housing with particularly small dimensions, consisting of at least two wafers, a cover wafer and a central wafer comprising multiple infrared-sensitive sensor pixels on a respective thin slotted membrane over a heat-insulating cavity is disclosed. A method for producing a high-resolution monolithic silicon micromechanical thermopile array sensor using wafer level packaging technology, wherein the sensor achieves a particularly high spatial resolution capability and a very high filling degree with very small housing dimensions, in particular a very low overall thickness, and can be inexpensively produced using standard CMOS processes. This is achieved in that the cover wafer is first rigidly mechanically connected to the provided central wafer comprising the sensor pixels with the infrared-sensitive pixels by means of wafer bonding, and the central wafer is then thinned out from the wafer rear face to a specified thickness.