Course Goal: Multidisciplinary learning and entrepreneurship Micro/nanotechnology

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

Course Structure: project based course

• Two quarter sequence

• Spring
• Predesigned masks, device and process
• Lab teams assigned for diversity of majors and backgrounds
• Qualify on equipment in Stanford Nanofab
• Summer
• Defined 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 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

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

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

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

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

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

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

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

Complete Experimental Setup: Force-Displacement Contact Measurements

Design

• Cantilever Beam

• Equivalent spring constant, K (N/m)

• Goal: maximize range and sensitivity

• Constraints

• 100 micron travel in 5nm steps (actuator selection)

Design Space

Design Space

Comparison to AFM cantilever

Cantilever Fabrication (omit gold pads!)

Processing: alignment

Processing: protective oxide

Processing: piezoresistors

Processing: conductors

Processing: oxide/anneal

Processing: contacts

Processing: DRIE

Cantilever Fabrication (shown w/ gold)

Cantilever SEM

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!

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

Interconnect Levels: wire bonding to dip package

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

Cantilever Calibration: time & frequency

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

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

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)

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

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