Shaping the Future of MEMS and Sensors
September 10, 2013
Challenges of MEMS Integration into
Medical Solutions
Alissa M. Fitzgerald, Ph.D., Founder and Managing Member
10th
anniversary
Outline
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About AMFitzgerald
Why MEMS are exciting for medical applications
Package integration
Environmental challenges
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Mission: Your Partner in MEMS Product Development
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Complete MEMS solutions, from concept to production
Technology
Design
Strategy
Simulation
Prototyping
& Process Low Volume
Integration Production
AMFitzgerald in-house
Package
& Test
Foundry
Production
Strategic partners
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MEMS solutions for OEMs and system integrators
• MEMS devices customized to
your application
– ISO-certified foundries
– Cost-effective production using
proven processes
– Fast time to market
• Customer supplies sensor spec
• AMFitzgerald delivers chips
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Medical applications are a growing part of our business
Types of MEMS
developed in 2012:
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Why MEMS are exciting for medical applications
Why MEMS are exciting for medical applications
• Biologically-compatible size scales
– 2-100 micron-sized features are easy to make
• Biocompatible materials
• Low-power, tiny sensors (0.3 – 4 mm)
• Pressure and motion data clinically useful
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Why MEMS are exciting for medical applications
• Wide range of uses, from lab bench to
patient monitoring
– Cell culture
– Proteomics/genomics/drug discovery
– Consumer-grade wearable health
monitors
– Point of care diagnostics
– Clinical-grade wearable health monitors
– Invasive short term diagnostics
– Surgical tools
– Implantable functions and diagnostics
Increasing
Product
Complexity
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Sophisticated capability in small form factor
• System integration
– Sensor(s)
– Signal processing and
analysis
– Battery-less operation
(power/read)
– Telemetry for medical sensor
network (with cell phone)
MEMS
sensor
Source: IMD
Stacked
MEMS and
ASIC chips,
wirebonded
Source: Chipworks/Kionix
Source: Proteus Biomedical
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Many potential implantable, invasive and wearable uses
Implantable pressure sensor
Invasive sensor
Source: CardioMEMS
Wearable health monitoring
Source: Sensimed
Source: Nike
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Second Sight: Argus II Retinal Prosthesis
• FDA approved
• Electrical stimulation
of retina for macular
degeneration
• MEMS microneedle
electrodes
• www.2-sight.com
Source: Second Sight
Source: NYTimes
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St. Jude Medical: Cardiology Guidewires
• PressureWire Aeris
– Fractional flow reserve
measurements (pressure
drop across coronary artery
stenosis)
– Better results than
angiography
– Also temperature, flow
– Stent or balloon treatment
Sensor location
0.36mm O.D.
Source: St.Jude Medical PressureWire with AgileTip
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Debiotech: Insulin Pumps
• NanopumpTM: volumetric
pump for insulin delivery
• Manufacturing
partnership with
STMicroelectronics
• www.debiotech.ch
Source: Debiotech SA
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Sensimed: Triggerfish IOP monitor
• Continuous intraocular pressure
(IOP) measurement for glaucoma
diagnosis
• Disposable lens
• Strain gage with wireless telemetry
• Under evaluation in Europe
• www.sensimed.ch
Recorder syncs with doctor’s
computer via Bluetooth
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Package integration challenges
Typical MEMS architectures
Membrane device:
Pressure
Force
Sound
Pump/Valve
Electrostatic comb device:
Accelerometer
Gyroscope
Actuator - position
Resonator
Electrostatic comb
fingers
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Wafer Dicing
• Similar to cutting tile
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Die attach and wire-bonding
• Methods were originally developed to attach chips to
rigid substrates (e.g. computers)
25 micron (1 mil) gold wire
Die attach epoxy
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Typical package architecture – pressure, microphones
Source: Freescale
pressure sensor
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Typical package architecture – motion sensors, resonators
Plastic encapsulation
No encapsulation
Source: Chipworks, STMicroelectronics
Cap hermetically
seals the MEMS
device
Source: CEA-Leti
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Challenge of packaging MEMS for invasive medical use
Flexible, round tube
Rigid, brittle
rectangle
Sensor
Flexible substrate
Package solution will be application-specific
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Environmental challenges:
implantable and single-use devices
Specific medical environmental challenges
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Temperature
Mechanical strain
Light
Moisture
Radiation
Magnetic fields
Sterilization
Hermeticity
Fracture
Electrical interconnect
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General environmental challenges for MEMS
• Every MEMS sensor will, to some degree, also sense:
– Temperature
– Mechanical strain
• Many MEMS sensors are also sensitive to light
• Temperature and light effects can be addressed with
compensation
• Dealing with strain-related effects much trickier
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Magnetic fields
• MRI fields can induce eddy
currents in MEMS chip
– Localized heating
– Spurious readings
• Custom design needed for use
in MRI fields
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Sterilization
• Gamma, e-beam: damaging to electronics and some
plastics
• Ethylene oxide: can be absorbed by plastics
• Steam 121-134 °C: creates problems with material CTE
mismatch, glass transition temperature
• Sterilization method must be considered during MEMS
and package design
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Hermeticity
• For invasive and implant applications:
– Sealing needed for biocompatibility
Silicon and oxides not fully compatible for implant
– Electrical interconnect metals (other than gold) not
compatible
• Medical device design expertise should inform MEMS
design choices
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Fracture protection
• Silicon is a brittle material
• Microneedles, probes
– Breakage can occur during rough
handling
– Encapsulation needed to prevent
piece migration
Biocompatible polymers
• Vibration and shock protection
– Can be addressed at chip and
assembly levels
Source: AMFitzgerald
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Electrical interconnect
Implantable and invasive applications will benefit from
through silicon via (TSV) technology
With TSV
Traditional assembly
Larger die needed
for bond pad area
Direct chip-to-flex bond
Wirebonds make
hermetic sealing
difficult
Can be surface mounted,
no wire bonding
Substrate for
electrical
interconnect
Wire pigtail
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Challenges in MEMS for invasive medical applications
• Buy vs. Make
– Lots of MEMS sensors available off the shelf
Low prices ($0.10 - $2.00 per sensor)
Reliability data available
Many IDMs restrict use in medical applications
Generally sized/spec’d for consumer electronics apps
– Custom MEMS design attractive, but:
Low volume MEMS have high unit costs (> $5 per sensor)
Environmental and reliability qualification testing is expensive
Long development (> 3 years) and expensive:
– Simple sensor > $2M
– Complex sensor with ASIC > $10M
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Challenges in MEMS for invasive medical applications
• Packaging, packaging, packaging
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Typically > 70% of finished unit cost
ASIC, electrical interconnect and leads
Environmental issues
“Square peg in round hole” problem
• Quality vs. production volume
– Need to run > 100 wafers/year to maintain quality standards
and repeatability
– Specialty medical devices might only need 10 wafers/year
Unit cost will be high
Yield low
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Summary
• MEMS sensors present a huge opportunity for medical
devices, particularly for invasive and implantable uses
– Sophisticated sensor functions
– Electronics system integration
• Medical environment, usage must inform design choices
– MEMS customization may be needed for certain medical
applications
• Challenges primarily remain in packaging and assembly
– Solutions will be specific to usage and form factor
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Contact
• Alissa Fitzgerald: amf@amfitzgerald.com
• 650 347 MEMS x101
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