Electrostatic Transfer Head for Micro Device Bonding
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Solution Overview
Problem
Integration and packaging of micro devices such as RF MEMS microswitches, LED display and lighting systems, and quartz-based oscillators are hindered by existing transfer and bonding technologies, which often require wafer bonding and de-bonding steps, and are inefficient in handling arrays of micro devices.
Innovation Solution
The use of electrostatic transfer head assemblies to pick up, transfer, and bond arrays of micro devices to a receiving substrate using energy transfer for bonding, which can involve thermal bonding, thermocompression bonding, eutectic alloy formation, or solid state diffusion, allowing for efficient integration and assembly of micro devices onto various substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional wafer bonding and de-bonding steps are used for transferring micro devices, then devices can be transferred from source to receiving wafer, but the process becomes complex and time-consuming due to multiple bonding and de-bonding steps
Solution Approach 1:
The patent extracts the bonding step from the transfer process by using a sacrificial layer that enables direct release of micro devices onto the receiving substrate without requiring de-bonding steps. The sacrificial layer is removed chemically or mechanically, allowing devices to be transferred in a single bonding operation.
Solution Approach 2:
The patent introduces a sacrificial layer as an intermediary between the source substrate and micro devices. This layer facilitates easy release of devices onto the receiving substrate by being selectively removable, thereby simplifying the transfer process and eliminating complex de-bonding steps.
2Adaptability or versatility
If elastomeric stamps with posts are used for transfer printing, then devices can be picked up and transferred, but the process requires intimate contact and van der Waals bonding which limits applicability
Solution Approach 1:
The patent replaces the mechanical van der Waals bonding mechanism with chemical bonding through sacrificial layers. This substitution eliminates the need for intimate contact and complex stamp mechanisms, allowing for more versatile and easier operation across different device types and substrates.
Solution Approach 2:
The patent changes the bonding mechanism from physical adhesion (van der Waals forces requiring intimate contact) to chemical bonding through sacrificial layer removal. This parameter change in bonding methodology increases adaptability while reducing operational complexity.
3Quantity of substance
If arrays of micro devices are transferred using traditional methods, then devices can be moved in bulk, but thermal cycling and mechanical deformation issues arise during the process
Solution Approach 1:
The patent performs preliminary bonding of micro devices to the receiving substrate through sacrificial layer removal before any thermal cycling or mechanical processing. This preliminary action secures devices in their final positions, preventing deformation and maintaining integrity during subsequent processing steps.
Solution Approach 2:
The sacrificial layer acts as a cushioning mechanism that protects micro devices from thermal stress and mechanical deformation during transfer. By enabling gentle chemical release rather than forceful mechanical separation, it prevents device damage while handling large arrays.
4Productivity
If electrostatic transfer head assembly is used to pick up and bond micro devices, then rapid transfer can be achieved, but energy transfer for bonding must be precisely controlled
Solution Approach 1:
The patent implements feedback control in the electrostatic transfer head assembly by monitoring and adjusting the voltage applied to electrostatic actuators during bonding. This feedback mechanism ensures precise energy transfer, achieving rapid transfer while maintaining exact bonding parameters for reliable device attachment.
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
Enables rapid transfer and bonding of micro devices to substrates in a matter of seconds, with the ability to handle large arrays and mitigate issues like thermal cycling and mechanical deformation, while forming viable electrical bonds.
Implementation Method 1
picking up an array of micro devices from a carrier substrate with an electrostatic transfer head assembly
Implementation Method 2
transferring energy from the electrostatic transfer head assembly to bond the array of micro devices to the receiving substrate, and releasing the array of micro devices onto the receiving substrate
Implementation Method 3
heat can be transferred from the electrostatic transfer head assembly, carrier substrate holder, or receiving substrate holder
Implementation Method 4
the transfer of energy causes solid state diffusion between the micro device bonding layer and the receiving substrate bonding layer
Data Source
AI summary
Electrostatic transfer head array assemblies and methods of transferring and bonding an array of micro devices to a receiving substrate are described. In an embodiment, a method includes picking up an array of micro devices from a carrier substrate with an electrostatic transfer head assembly supporting an array of electrostatic transfer heads, contacting a receiving substrate with the array of micro devices, transferring energy from the electrostatic transfer head assembly to bond the array of micro devices to the receiving substrate, and releasing the array of micro devices onto the receiving substrate.