1. New Trends and Technologies for (N)MEMS
Michael Kraft

2. Overview Innovation sources for MEMS devices
requirements for doing MEMS
novel fabrication processes
innovative design of micromachined structures
system integration
Key technologies for future MEMS devices
Precision wafer bonding
Metrology and characterization
Conclusions

3. Requirements for ‘Doing’ MEMS
A reasonable clean cleanroom
Flexibility to introduce new materials
Not having to worry about contamination
Reasonable good lithography (~1um)
Some special tools…
Good metrology and measurement equipment
Southampton just opened a £80m facility with state of the art equipment

4. Southampton Nanofabrication Centre
Micro
Flexible nanotechnology clean room
Silicon, glass, thin film technologies
680m2 clean room (class 100 & 1000)
110m2 bioMEMS clean room (class 10000)
110m2 thick film clean room (class 1000)
People
14 academic staff
6 clean room engineers
50+ researchers
50+ project students
… and many, many collaborators
Carbon Nanotube
bundles
Si nanobridge with a single quantum dot
cavity

5. Research Themes Lab-on-a-Chip Micro & Nano Electromechanical Systems
Nanoelectronics
Nanophotonics
Quantum Information Technology
Silicon Photovoltaics
NEMS bridge as mechanical memory
TEM sample preparation in a FIB

6. Innovation by Process Development
MEMS has revolutionized sensors/actuators by making them small, low power, affordable through batch fabrication.
Success stories include: pressure sensors, accelerometers, gyroscopes, flowsensors, etc.
Past examples of process innovation: DRIE etching – the Bosch process.
STS Pegasus DRIE etcher

7. New Process Technology Example: Ultra-smooth Optical Cavities
Optical fibre
Optical cavities can be used to detect single atoms
Applications in quantum information technology
Process technology challenge: cavities need to be ultra-smooth

8. Fabrication Process
A silicon substrate with 100nm of oxide deposited and patterned
100nm of silicon nitride is deposited and patterned
The silicon nitride is stripped using orthophosphoric acid
The silicon is etched using a HF based solution
The resist is removed creating the finished chip
3µm of Gold is sputtered
Photoresist is spun and patterned and the gold is ion beam milled
The silicon is etched using an ASE isotropic etch
A 50nm Chromium and 100nm Gold layer is sputtered
Photoresist is spun and patterned
Silicon
Innovation through novel combination of existing processes
Chromium
Silicon oxide
Photoresist
Gold
Silicon nitride

9. Process Optimization
Various etch rates can be used to make any radius of curvature
Longer etch rates gives smoother mirrors
Achieved around below 1nm rms roughness

10. Novel Design Approach for MEMS Example: Mechanical amplification
Most MEMS sensors rely on tiny deflections of a proof mass
The deflection is detected electronically by measuring a change in capacitance
Innovation: introduce a mechanical amplification stage
This is based on a simple leverage mechanism

11. Novel Design Approach for MEMS Example: Mechanical amplification

12. System Integration for MEMS Example: electromechanical control systems
MEMS gyroscope (collaboration with Peking University)
Micromachined sensing element incorporated in an electromechanical sigma-delta modulator
This forms a force-feedback system with advantages over an open loop system
Better linearity, dynamic range, bandwidth, direct digital output

13. Bandpass SDM Interface for a MEMS Gyro
Spectra of simulated and measured results agree well
Reduced sampling frequency compared to low-pass architecture
SNR of 92dB with full scale input
‘Butterfly’ sensing element from SensoNor, Norway.

14. Atom Chip: Multi domain integration
Electrostatic xy comb drive
Electrostatic z parallel plate
Tuneable optical cavity
Bose-Einstein atom cloud
High current density gold wires
Silicon
Fibre gold coated at the tip

15. Atom Chips Fundamental research New devices – precise sensors
Devices for trapping and manipulation of atoms on integrated microchips.
Quantum laboratories on chip.
Fundamental research
Quantum behaviour
Low dimensional physics
Entanglement and coupling
New devices – precise sensors
Atom interferometers
Atomic clocks
Accelerometers/Gyroscopes
Quantum information processing
Quantum computers

16. Overview Innovation sources for MEMS devices
requirements for doing MEMS
novel fabrication processes
innovative design of micromachined structures
system integration
Key technologies for future MEMS devices
Precision wafer bonding
Metrology and characterization
Conclusions

17. Aligned Bonding for Multi Wafer MEMS
EVG 520 bonder
EVG 620 double sided mask aligner
Conventional approach: Aligner - bonder
For example from EVG
Accuracy ~1um

18. (Nano) Alignment Bonding
‘LEGO on a chip’
SEM image of aligned and
bonded chips.
self-engaging alignment concept
using cantilevers
Vernier structures to evaluate
bonding alignment
IR image of a bonded sample
2.3mm
Demonstrated 200nm alignment bonding at chip level
Only 10% of wafer area required for self-engaging structures
Wafer surface smooth enough for thermo-compression bonding

19. ‘Repairing’ of N/MEMS: Focussed Ion Beam
Zeiss NVISION40 FIB
Machining of complex 3D structures
Prototype post-processing

20. ‘Repairing’ of N/MEMS: Focussed Ion Beam

21. Characterization of MEMS
Polytec MSA400 MEMS dynamic tester
In plane and out of plane dynamic measurements
White light interferometer
2D electrostatic actuator

22. Characterization of MEMS

23. Characterization of MEMS
Polytec MSA400 MEMS dynamic tester
In plane and out of plane dynamic measurements
White light interferometer
Investigation of levitation forces

24. Characterization of MEMS

25. High-res imaging: He Ion Microscope
Orion image of CNTs 200nm bar
Description
Zeiss Orion He ion microscope
- Resolution <0.9nm
- High depth of focus
- High material contrast
- Rutherford backscattering analysis:
element identification
- Nanoengineering
Orion image of CNTs 100nm bar
Orion image of CNTs 50nm bar

26. Conclusions Multi-functional MEMS is becoming mainstream
MEMS is in a transition to system-on-chip or system-in-a-package (micro-system-technology)
There are few really novel fabrication processes on the horizon
Rather new combinations of existing processes
There are still plenty of new design concepts to be explored
There are new characterization tools which are making an impact
The next BIG thing:
INTEGRATION INTEGRATION INTEGRATION