New Trends and Technologies for (N)MEMS

Michael Kraft

Overview

Innovation sources for MEMS devices requirements for doing MEMSnovel fabrication processes innovative design of micromachined structures

system integration

Key technologies for future MEMS devices Precision wafer bonding Metrology and characterization

Conclusions

Requirements for ‘Doing’ MEMSA reasonable clean cleanroomFlexibility to introduce new materialsNot having to worry about contaminationReasonable good lithography (~1um)Some special tools…Good metrology and measurement equipment

Southampton just opened a £80m facility with state of the art equipment

Southampton Nanofabrication CentreMICRO

Flexible nanotechnology clean roomSilicon, glass, thin film technologies

680m2 clean room (class 100 & 1000)110m2 bioMEMS clean room (class 10000)110m2 thick film clean room (class 1000)

People14 academic staff6 clean room engineers50+ researchers50+ project students

… and many, many collaborators

Carbon Nanotube bundles

Si nanobridge with a single quantum dot cavity

Research ThemesLab-on-a-ChipMicro & Nano Electromechanical SystemsNanoelectronicsNanophotonicsQuantum Information TechnologySilicon Photovoltaics

NEMS bridge as mechanical memory TEM sample preparation in a FIB

Innovation by Process DevelopmentMEMS 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

New Process TechnologyExample: Ultra-smooth Optical Cavities

Optical cavities can be used to detect single atomsApplications in quantum information technologyProcess technology challenge: cavities need to be ultra-smooth

Opt

ical

fibr

e

A silicon substrate with 100nm of oxide deposited and patterned100nm of silicon nitride is deposited and patternedThe silicon is etched using a HF based solutionThe silicon nitride is stripped using orthophosphoric acidThe silicon is etched using an ASE isotropic etchA 50nm Chromium and 100nm Gold layer is sputteredPhotoresist is spun and patterned 3µm of Gold is sputteredPhotoresist is spun and patterned and the gold is ion beam milledThe resist is removed creating the finished chip

Silicon

Silicon oxide

Chromium

Gold

Photoresist

Silicon nitride

Fabrication Process

Innovation through novel combination of existing processes

Process Optimization

Various etch rates can be used to make any radius of curvatureLonger etch rates gives smoother mirrorsAchieved around below 1nm rms roughness

Novel Design Approach for MEMSExample: Mechanical amplification

Most MEMS sensors rely on tiny deflections of a proof massThe deflection is detected electronically by measuring a change in capacitanceInnovation: introduce a mechanical amplification stageThis is based on a simple leverage mechanism

Novel Design Approach for MEMSExample: Mechanical amplification

System Integration for MEMSExample: electromechanical control systems

Micromachined sensing element incorporated in an electromechanical sigma-delta modulatorThis forms a force-feedback system with advantages over an open loop systemBetter linearity, dynamic range, bandwidth, direct digital output

Sensing element

xC +

Coriolisforce

CV

Electrostatic feedback

force

Pick-off circuit Phasecompensator

Electronic resonators1 bit A/D

fsOutput bitstream

Elec. 1 bit D/AD

A

+

Elec. 1 bit D/AD

A

Vfb

Reference voltage

+

MEMS gyroscope (collaboration with Peking University)

Spectra of simulated and measured results agree wellReduced sampling frequency compared to low-pass architectureSNR of 92dB with full scale input

‘Butterfly’ sensing element from SensoNor, Norway.

Bandpass SDM Interface for a MEMS Gyro

High curre

nt den

sity g

old wire

s

Electrostatic xy comb driveElectrostatic z parallel plate

Fibre gold coated at the tip

SiliconBose-Einstein atom cloud

Tuneable optical cavity

Atom Chip: Multi domain integration

Devices for trapping and manipulation of atoms on integrated microchips.

Quantum laboratories on chip.

Fundamental research Quantum behaviourLow dimensional physicsEntanglement and coupling

Atom Chips

New devices – precise sensorsAtom interferometersAtomic clocksAccelerometers/GyroscopesQuantum information processingQuantum computers

Overview

Innovation sources for MEMS devices requirements for doing MEMSnovel fabrication processes innovative design of micromachined structures

system integration

Key technologies for future MEMS devices Precision wafer bonding Metrology and characterization

Conclusions

Aligned Bonding for Multi Wafer MEMS

Conventional approach: Aligner - bonderFor example from EVGAccuracy ~1um

EVG 620 double sided mask aligner

EVG 520 bonder

(Nano) Alignment Bonding

Demonstrated 200nm alignment bonding at chip levelOnly 10% of wafer area required for self-engaging structuresWafer surface smooth enough for thermo-compression bonding

self-engaging alignment conceptusing cantilevers

SEM image of aligned andbonded chips.

Vernier structures to evaluate bonding alignment

IR image of a bonded sample

2.3mm

‘LEGO on a chip’

‘Repairing’ of N/MEMS: Focussed Ion Beam

Zeiss NVISION40 FIBMachining of complex 3D structures

Prototype post-processing

‘Repairing’ of N/MEMS: Focussed Ion Beam

Characterization of MEMS

Polytec MSA400 MEMS dynamic testerIn plane and out of plane dynamic measurementsWhite light interferometer

2D electrostatic actuator

Characterization of MEMS

Characterization of MEMS

Polytec MSA400 MEMS dynamic testerIn plane and out of plane dynamic measurementsWhite light interferometer

Investigation of levitation forces

Characterization of MEMS

High-res imaging: He Ion Microscope

Orion image of CNTs 50nm 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 200nm bar

Orion image of CNTs 100nm bar

ConclusionsMulti-functional MEMS is becoming mainstreamMEMS 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 horizonRather new combinations of existing processesThere are still plenty of new design concepts to be exploredThere are new characterization tools which are making an impactThe next BIG thing:INTEGRATION INTEGRATION INTEGRATION