Compressible Pillar Stops for Uniform Quantum Chip Spacing
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Solution Overview
Problem
In quantum computing, achieving precise and uniform chip-to-chip separation in stacked devices is challenging due to variations in substrate bonding, leading to inconsistencies in qubit coupling and increased decoherence.
Innovation Solution
The use of pillars as compressible stops between substrates, which expand to match the thickness of bump bonds, ensuring a consistent separation distance and improving the precision and uniformity of electrical connections, while also providing potential electromagnetic insulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If substrate bonding is performed without pillars, then the bonding process is simpler, but the chip-to-chip separation distance becomes non-uniform and imprecise
Solution Approach 1:
Pillars are introduced as intermediary elements between the first and second substrates to precisely control and maintain the separation distance. These pillars act as mechanical stops that define the gap between substrates, ensuring uniform spacing while allowing the bonding process to proceed with improved precision.
Solution Approach 2:
The pillars enable precise control of the separation distance parameter by varying their height and compressibility. During bonding, the pillars compress to a target thickness, and their material properties (such as using softer materials like indium) allow them to deform controllably to achieve the desired final separation distance with high precision.
2Manufacturing precision
If pillars with larger cross-sectional area are used, then the separation distance precision improves, but the space available for bump bonds decreases
Solution Approach 1:
The pillar structure is segmented into multiple discrete elements distributed across the substrate rather than using a single large support structure. This segmentation allows the bonding area to be preserved in regions between pillars while still achieving overall separation distance control through the collective effect of multiple pillar stops.
3Manufacturing precision
If multiple pillars are used for precise separation control, then the separation uniformity improves, but the device complexity increases
Solution Approach 1:
The pillars serve multiple functions simultaneously: they act as mechanical stops to define separation distance, provide compression control during bonding, offer structural support, and can even serve as electrical interconnects or thermal management elements. This multi-functionality reduces the need for additional separate components.
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 repeatability, precision, and uniformity of substrate separation, improving the coupling between qubits and control circuit elements, reducing decoherence and energy loss, and enabling more efficient 3D integration of quantum circuit elements.
Implementation Method 1
applying a force between the first substrate and the second substrate to compress the multiple bump bonds to the same thickness as the thickness of the at least one pillar
Implementation Method 2
The expansion of the at least one pillar may be measured. For example, measuring the expansion of the pillar includes using an edge-view microscope to determine the amount of expansion
Data Source
AI summary
A stacked device including a first substrate that includes a quantum information processing device, a second substrate bonded to the first substrate, and multiple bump bonds and at least one pillar between the first substrate and the second substrate. Each bump bond of the multiple bump bonds provides an electrical connection between the first substrate and the second substrate. At least one pillar defines a separation distance between a first surface of the first substrate and a first surface of the second substrate. A cross-sectional area of each pillar is greater than a cross-sectional area of each bump bond of the multiple bump bonds, where the cross-sectional area of each pillar and of each bump bond is defined along a plane parallel to the first surface of the first substrate or to the first surface of the second substrate.