Planar Cavity MEMS Electrode Volume Adjustment
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Solution Overview
Problem
Existing MEMS structures with spin-on polymer cavities face issues such as non-planar surfaces, lithographic depth of focus variability, packaging reliability due to dielectric cracking, and organic residues, which affect the performance and reliability of MEMS devices.
Innovation Solution
The development of a method to form planar cavity MEMS structures using a sacrificial layer and a reverse damascene process, which involves adjusting the metal volume of electrodes to modify beam bending characteristics and reduce material variability, resulting in a flat or planar surface structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If spin-on polymer is used to form MEMS cavity, then cavity formation is achieved, but non-planar surface is created causing lithographic depth of focus variability
Solution Approach 1:
A planarization layer is deposited over the spin-on polymer cavity structure before subsequent lithographic processing. This preliminary planarization action creates a flat surface for photolithography while the cavity structure remains intact underneath, resolving the conflict between easy cavity formation and lithographic precision
2Ease of manufacture
If spin-on polymer is used to form MEMS cavity, then cavity formation is achieved, but dielectric cracking occurs reducing packaging reliability
Solution Approach 1:
A stress buffer layer is introduced as an intermediary between the spin-on polymer cavity and the overlying dielectric structures. This buffer layer absorbs and distributes mechanical stress, preventing stress transfer that would cause dielectric cracking and improving packaging reliability while maintaining the ease of cavity formation
3Temperature
If low temperature processing is used for spin-on polymer, then polymer damage is avoided, but organic residues remain in cavity
Solution Approach 1:
Oxygen plasma treatment is applied to chemically oxidize and remove organic residues from the cavity at low temperatures. This replaces the need for high-temperature thermal processing that would damage the polymer, using chemical oxidation instead to eliminate carbon-containing contaminants while preserving the polymer structure
4Ease of manufacture
If metal volume of electrodes is not adjusted, then manufacturing is simpler, but beam bending occurs due to stress
Solution Approach 1:
The metal volume of electrodes is adjusted by modifying deposition thickness or area parameters during fabrication. This parameter change compensates for intrinsic stress in the electrode materials, balancing the beam structure to prevent bending while maintaining manufacturability through controlled deposition process adjustments
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 reduces overall stress and material variability in MEMS devices, improving their reliability and performance by eliminating non-planar surfaces and associated issues, while enabling the creation of devices like single or dual wire beam contact switches and air gap inductors.
Implementation Method 1
a cantilever arm (suspended electrode with one end fixed) is pulled toward a fixed electrode by application of an actuation voltage. The voltage required to pull the suspended electrode to the fixed electrode by electrostatic force is called pull-in voltage
Data Source
AI summary
A method of forming a Micro-Electro-Mechanical System (MEMS) includes forming a lower electrode on a first insulator layer within a cavity of the MEMS. The method further includes forming an upper electrode over another insulator material on top of the lower electrode which is at least partially in contact with the lower electrode. The forming of the lower electrode and the upper electrode includes adjusting a metal volume of the lower electrode and the upper electrode to modify beam bending.