Upload
chelsey-baye
View
225
Download
7
Tags:
Embed Size (px)
Citation preview
AIM Industrial Advisory Committee Meeting 7 April 2004
Beth PruittAssistant Professor
Dept. of Mechanical Engineering
Stanford University
http://me342.stanford.edu
Course Development:ME342 MEMS Laboratory
AIM Industrial Advisory Committee Meeting 7 April 2004
Course Goal: Multidisciplinary learning and entrepreneurship • Micro/nanotechnology
–Scaling laws–Transduction mechanisms
• Design/manufacturing–Processes and tolerances–Material selection and limitations– Innovation
• Biomedical device engineering–Biocompatibility–Safety/Ethics
• Multidisciplinary language
AIM Industrial Advisory Committee Meeting 7 April 2004
Course Structure: project based course
• Two quarter sequence–Spring
Predesigned masks, device and processLab teams assigned for diversity of majors and backgroundsQualify on equipment in Stanford Nanofab
–SummerDefined projects with partners (design starts early May)Complete design, fabricate, and test cycle
• Partners– Internal research collaboration needs (e.g.
Cardiology, Material Science, Cell Physiology)– Industry defined challenges (e.g. Intel, Honeywell)
AIM Industrial Advisory Committee Meeting 7 April 2004
AIM Course Development Funding
• $10,000 grant to help start this course–Winter quarter TA support to debug the process
and prepare course materials–Prototyping supplies (wafers, masks, etc.)–Thank you!
• I gratefully acknowledged assistance this quarter that also came from:–Nu Ions: donation of ion implant service for course–Center for Integrated Systems: new user grants to
fund team clean room charges
• Goal is self-sustaining course model
AIM Industrial Advisory Committee Meeting 7 April 2004
Day 1
• About 70 students attended the first class
• 20 students were admitted based on questionnaires of background and interests
• 4 teams of 5 (max. capacity this year) formed with at least 1 EE, 1 Med/Phys/Chem/MSE, and 2-3 ME students (will cross-list in EE, not advertised this time)
• 1 team of 5 “overqualified” applicants accepted to audit A and participate fully in B
• Very tough to turn students away, an exciting amount of interest in microfabricated solutions for new areas of research exists at Stanford
AIM Industrial Advisory Committee Meeting 7 April 2004
Week 1
• Safety training sessions for all new students to
obtain clean room access
• Safety tours of SNF (Stanford NanoFab Facility)
• Written safety test
• Cleanliness training
• Instill sense of MEMS/clean room community
AIM Industrial Advisory Committee Meeting 7 April 2004
Week 2-6: Processing
• Fabrication in earnest under wing of senior MEMS
research students for 4 weeks
• Incredible SNF staff support to ensure thorough
qualification of students as users
• 2 weeks and 2 masks as independent users (with
support net of teaching team)
• Analysis/simulation in parallel with fabrication
Week 7-9: Measurements• Package, test, signal condition and calibrate
• Compare theory and experiment
AIM Industrial Advisory Committee Meeting 7 April 2004
ME342A MEMS LaboratoryQ1 Project: Fabrication and Testing of Piezoresistive Cantilevers for nN-mN Force Measurement
Beth PruittDept. of Mechanical Engineering
Stanford University
AIM Industrial Advisory Committee Meeting 7 April 2004
Background for Project
• Sensors designed as part of a MEMS based
system for force-displacement measurements
of electrical microcontacts
• Sensors originally incorporated gold contact
pad at tip to study thin gold films as
MEMS/micro-electrical contacts
AIM Industrial Advisory Committee Meeting 7 April 2004
MicroContact example under study:Formfactor MicroSpringTM Interconnects
• 1st and 2nd level interconnect –pressure connection from the die to the printed circuit board, e.g. 2-sided memory module
with permission
AIM Industrial Advisory Committee Meeting 7 April 2004
Trends and opportunities: Separable Contacts for Packaging, Testing, Switching
• Shrinking interconnect pitch and size– Smaller probes for test– Smaller off-chip interconnects
• Thinner wafers and organic dielectrics– Low force probing– Thinner metal stackups
• To support continued miniaturization need low force,
small size, and low contact resistance
AIM Industrial Advisory Committee Meeting 7 April 2004
Design of Contact Characterization Sensors• Measurement over 6! orders
of magnitude (2 designs)
• Fabrication of thin film metals
in-situ with standard
processing (evaporated,
sputtered, plated)
• 4-wire contact resistance
measurement
• Measure force and contact
resistance simultaneously
Gold Pad
Piezoresistor
measurement leads
AIM Industrial Advisory Committee Meeting 7 April 2004
Complete Experimental Setup:Force-Displacement Contact Measurements
Piezoactuator and controller
GPIB cardLaptop with Labview
DAQ card
Voltage Measurements(7 Channels)
AIM Industrial Advisory Committee Meeting 7 April 2004
Design
• Cantilever Beam– Equivalent spring constant, K (N/m)
• Goal: maximize range and sensitivity
• Constraints100 micron travel in 5nm steps (actuator selection)
w
t
L
P
001.06
2≤=
wEtLPε
1.06
3
2
≤=EwtPLθ
3
3
4L
wEtK =
Piezoresistor linearity with strain (Matsuda & Kanda)
Linear elastic beam equations (Young)
z
x
P=Kz
AIM Industrial Advisory Committee Meeting 7 April 2004
1E-01
1E+00
1E+01
1E+02
1E+03
1E+04
1E-04 1E-03width(m)
Design Space
A = require L > w
B= piezo ε limited
C= linear elastic θ limited
D = cantilever design 1
800µm x 3mm x 40µm
K= 85 N/m
1E+01
1E+00
1E-01
1E-02
1E-03
1E-04
Kmin (N/m)
L max(m)
B
C
D
40µm thick cantileverPmax @ 100 µm =10mN
A
L max(m) Kmin (N/m)
AIM Industrial Advisory Committee Meeting 7 April 2004
1E-04
1E-03
1E-02
1E-01
1E+00
1E+01
1E-04 1E-03width(m)
Design Space
A = require L > w
B= piezo ε limited
C= linear elastic θ limited
E = cantilever design 2
400µm x 6mm x 25µm
K=1.3 N/m
Kmin (N/m)
L max(m)
B
25µm thick cantileverK ~ 1.3 N/mPmax = 0.6mN
A
L max(m) Kmin (N/m)
E
AIM Industrial Advisory Committee Meeting 7 April 2004
Comparison to AFM cantilever
Park Scientific dlevers ™K from 1.3 to 16 N/m
Small displacement range
3.6mm
1.6mm
L = 180 mW = 35 mt = 2 m
K = 1.3 N/m
L= 6 mmW= 400 mt = 25 m
K = 1.3 N/m
L
W
Custom CantileversK from 1.3 to 85 N/m
100m displacement range
AIM Industrial Advisory Committee Meeting 7 April 2004
Cantilever Fabrication (omit gold pads!)
doped piezoresistor, B+
doped conductor, B++ aluminum
siliconSiO2
silicon
aluminum
piezoresistor
conductor
7 mask process: 25 micron SOI, 300micron handle
AIM Industrial Advisory Committee Meeting 7 April 2004
Processing: alignment
Pattern resist and light Si etch (3000 angstroms) to define alignment patterns
KEY:SiliconOxideResistPiezoresistor dopingConductor dopingInterconnect Metallization (Al)
AIM Industrial Advisory Committee Meeting 7 April 2004
Processing: protective oxide
Strip resist
Grow protective screeening oxide ~250 angstroms
KEY:SiliconOxideResistPiezoresistor dopingConductor dopingInterconnect Metallization (Al)
AIM Industrial Advisory Committee Meeting 7 April 2004
Processing: piezoresistors
Pattern resist
50 keV boron implant for piezoresistors, e.g. dose = 1e15 ions/cm2
KEY:SiliconOxideResistPiezoresistor dopingConductor dopingInterconnect Metallization (Al)
AIM Industrial Advisory Committee Meeting 7 April 2004
Processing: conductors
Pattern resist
50 keV boron implant for piezoresistors, dose = 1e16 ions/cm2
KEY:SiliconOxideResistPiezoresistor dopingConductor dopingInterconnect Metallization (Al)
AIM Industrial Advisory Committee Meeting 7 April 2004
Processing: oxide/anneal
Strip damaged oxide
Wet Oxidation 900C, ~2500A, 2 m depth, piezo ~ 130 / , conductors ~ 45 /
KEY:SiliconOxideResistPiezoresistor dopingConductor dopingInterconnect Metallization (Al)
AIM Industrial Advisory Committee Meeting 7 April 2004
Processing: contacts
Open oxide
Strip Resist
Sputter 0.5 m Aluminum
Pattern and etch Al
KEY:SiliconOxideResistPiezoresistor dopingConductor dopingInterconnect Metallization (Al)
AIM Industrial Advisory Committee Meeting 7 April 2004
Processing: DRIE
Frontside Etch- 1.6 m resist, open oxide, etch Si to buried oxide, 1.6 m resist frontside protect
KEY:SiliconOxideResistPiezoresistor dopingConductor dopingInterconnect Metallization (Al)
Backside Etch-, 10m resist, open oxide, etch Si to buried oxide, wet etch box
AIM Industrial Advisory Committee Meeting 7 April 2004
Cantilever Fabrication (shown w/ gold)
doped piezoresistor, B+
doped conductor, B++ aluminumgold
siliconSiO2
aluminum
conductor piezo
gold
AIM Industrial Advisory Committee Meeting 7 April 2004
Cantilever SEM
AIM Industrial Advisory Committee Meeting 7 April 2004
ME342 Cantilevers-7 Masks, no Gold
• Mask Levels 1-3 completed by TA’s–Alignment Marks/Cantilever outline–Conductive Interconnect Implants–Piezoresistive Region Implants
• Team Processing Mask Levels 4-7 –Complete in Labs 2-6 plus some time outside of lab
for levels 6 and 7–Qualify individually on wetbenches, litho, DRIE
during labs of ME342–Note: team stuck at mask 5 until all team members
qualify on required equipment!
AIM Industrial Advisory Committee Meeting 7 April 2004
ME342 Processing
• Each team completes processing with same
mask set
• Each team has 5-6 wafers to process–2 SOI wafers fully released by DRIE (300µm)–3 test wafers partially processed (Noise only)
• Sensor measurements, 2 die per person–Packaging and Signal Conditioning–Testing and Measurements (Sensitivity & Noise)
• Analysis
AIM Industrial Advisory Committee Meeting 7 April 2004
Interconnect Levels: wire bonding to dip package
0th level interconnect1st level interconnect
2nd level interconnect
Printed circuit board
Silicon die
Package
AIM Industrial Advisory Committee Meeting 7 April 2004
Cantilever Calibration
• Piezoresistor Bridge Voltage vs. Displacement – Measure at resonant frequency of cantilever– Typical sensitivity ~ 1mV/µm
• Noise spectrum of piezoresistor– < 0.1µV/Hz or ~80pN/ Hz at 1Hz
15V
Laser vibrometer
Signal analyzer
Vdisplacement
Vstrain
AIM Industrial Advisory Committee Meeting 7 April 2004
Cantilever Calibration: time & frequency
effn m
K=ω
dceff mmm 24.0+=
ωn = 1st resonance
K = spring constant mc= concentrated mass
md= distributed mass
ω0
ω1
ω2
ω3
AIM Industrial Advisory Committee Meeting 7 April 2004
ME342A Analysis
• Simulate piezoresistor values (TSUPREM4)–Each wafer receives different dose/anneal set, each
student assigned a particular wafer to analyze
• Predict spring constant and gage factor
• Determine sensitivity and noise of cantilevers –compare analysis by beam equations and noise
characteristics to measurements
• Comparisons and Conclusions–15 min. talk 6/3, short report of results
AIM Industrial Advisory Committee Meeting 7 April 2004
ME342B Design Projects
• Project and team assignments early May
• Initial designs due end of May
• Mask designs must be submitted before start
of summer quarter!
• Processing and testing completed in ME342B
• Seminars, team meetings and lots of lab time
in summer quarter
• Project results = Conference papers???–e.g. MEMS’05, ASME’05, send 1 author per paper
AIM Industrial Advisory Committee Meeting 7 April 2004
Potential Projects for ME342B 2004
• Radial 100% strain gage for measuring deformation in animal model
blood vessels, e.g. rat aorta (Taylor, ME/cardiology)
• Integrated touch sensitivity system for neurological examination
(Goodman, molecular & cell physiology)
• Out-of-plane actuated stage (Intel mirror steering)
• Active thermal isolation package (Honeywell chip scale atomic clock)
• Implanted piezoresistor design rule formulation (Pruitt)
• Optimization of miniature blood pressure sensor sensitivity by
process and geometry (Feinstein, pediatric cardiology)
• Coupled beam microresonators for molecular assay (Melosh, MSE)
AIM Industrial Advisory Committee Meeting 7 April 2004
9 weeks to go and the whole Summer!
• A class full of enthusiasm
• The best teaching assistants anyone one
could ask for
• A supportive clean room environment and
technical staff
• A rich tradition of innovation in manufacturing
and design
• Cool projects inspired by local industry and
my Bio-X collaborators
AIM Industrial Advisory Committee Meeting 7 April 2004
Thank you AIM for your help and support!
• 2004-2005 MEMS projects wanted!
• Team of 3-4 multidisciplinary students May
plus summer
• Innovative ideas, unique facilities, excellent
coaching from faculty and industry
• Projects on the margin, something a company
would like to try or know if it works but doesn’t
have manpower, expertise, or resources for it