Wafer Bonding for Infrared Sensor Arrays
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Solution Overview
Problem
Existing methods for producing wafer bonds often result in increased reject likelihood due to the common processing of MEMS and ASIC structures over many mask planes, leading to inefficiencies and increased costs, and fail to maintain short distances between sensor pixels and evaluation circuits.
Innovation Solution
Separating ASIC and MEMS structures onto different wafers and bonding them using metal wafer contacts, allowing for optimized processing of each structure and minimizing area occupancy, while using diode elements for radiation detection and a cap wafer to maintain reduced pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If common processing of MEMS and ASIC structures over many mask planes is used, then integration of evaluation circuit and sensor array is achieved, but reject likelihood increases and manufacturing efficiency decreases
Solution Approach 1:
The patent divides the previously integrated wafer into two separate wafers: a first wafer for MEMS sensor array structures and a second wafer for ASIC evaluation circuit structures. This segmentation allows each wafer to be processed independently through their respective optimized fabrication processes without interfering with each other, thereby reducing the reject likelihood while maintaining the functional integration of both components in the final device.
2Device complexity
If common processing of MEMS and ASIC structures is used, then integration is achieved, but area occupancy increases
Solution Approach 1:
By segmenting the device into two separate wafers processed independently and then bonded together, each wafer can be optimized for its specific function with minimal area requirements. The MEMS sensor array wafer and ASIC evaluation circuit wafer can be fabricated with their respective optimal layouts without the need to accommodate both structure types on a single large substrate, thereby reducing overall area occupancy.
3Ease of manufacture
If separate wafers are used for MEMS and ASIC structures, then processing optimization and area occupancy are improved, but additional bonding steps are required
Solution Approach 1:
The patent employs self-aligned bonding techniques where metal bonding pads are automatically positioned relative to each other through precise wafer alignment during the bonding process. This self-service approach minimizes the need for additional complex alignment and bonding steps, as the bonding interfaces are designed to self-align, thereby reducing the overall process complexity despite using separate wafers.
4Ease of manufacture
If separate wafers are bonded together, then processing optimization is achieved, but maintaining short distances between sensor pixels and evaluation circuit becomes challenging
Solution Approach 1:
The patent uses a stacked configuration where the first wafer containing the MEMS sensor array is positioned directly above or below the second wafer containing the ASIC evaluation circuit. This nesting-like vertical arrangement minimizes the distance between corresponding sensor pixels and evaluation circuit elements by stacking the functional layers closely together, thereby maintaining short signal paths while allowing separate processing of each wafer.
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 reliable and cost-effective detection of electromagnetic radiation by allowing optimized processing of each wafer type, reducing external influences, and maintaining short distances between sensor pixels and evaluation circuits, while minimizing area occupancy and maintaining reduced pressure.
Implementation Method 1
the voltage at the diode element changes so that the temperature change of the sensor array caused by radiation can be deduced
Implementation Method 2
the sensor array is configured as a microbolometer array for registering the electromagnetic radiation, in particular far infrared radiation. In this way, a change in electrical resistance due to the electromagnetic radiation absorbed at the sensor array and leading to a temperature change in the sensor array can advantageously be registered.
Data Source
AI summary
An arrangement of at least two wafers for detecting electromagnetic radiation, in particular far infrared radiation, comprises a first wafer and a second wafer. The first wafer includes a microsystem formed as a sensor array. The microsystem is configured to register electromagnetic radiation and provide a corresponding sensor signal. The second wafer includes an integrated circuit formed as an evaluation circuit that is coupled to the sensor array. The integrated circuit is configured to detect the electromagnetic radiation with the aid of the sensor signal provided.