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New Tools and Methodology for MEMS Development June 2013 Steve Breit, PhD V.P. Engineering
New Tools and Methodology for MEMS Development
June 2013
Steve Breit, PhD V.P. Engineering
© Coventor, Inc. Confidential
Company Overview
History: Founded in 1996 with focus on MEMS design automation
• Software tools and design methodology • Expertise in 3D modeling and simulation • Proven track record in the MEMS industry
with worldwide, top-tier customer base
Today: Expanded offering to the MEMS and semiconductor industries with a unique process modeling solution
• Critical for advanced technology nodes: 22 nm CMOS and beyond, DRAM, Flash,…
• Multiple use cases: process development and integration, design rules, DFM, metrology,...
• Speed and Capacity far surpass alternative solutions
Apple iPad and iPhone Nintendo Wii
MEMS Market
Intel 22nm trigate transistors
Array of 9 8T SRAM cells in SEMulator3D
FinFET variability analysis
Semiconductor Market
Slide 2
New Tools & Methodology for MEMS Design
Overview • Motivation
• The Traditional Approach
• The New Approach
• Case Study: MEMS Varactor Manufacturability
• Conclusion & Discussion
© Coventor Inc. 2012 Slide 3
Bring MEMS to market still takes too long!
Reduce time-consuming “built-and-test” cycles
MEMS development still takes too long!
Use simulation to shorten
development time to market
Coventor Product Platform
© Coventor Inc. 2011 Slide 5
Process Development
Device Design
System-Level Optimization
CoventorWare®
SEMulator3D®
MEMS+® • Rapid concept
exploration • MEMS models for
system & IC design
• Multi-physics simulation
• Stress analysis • Damping effects • Packaging effects
• Virtual fabrication of MEMS & semi-conductor devices
• Silicon-accurate geometry
• Virtual metrology
• Sensitivity • Linearity • Frequency response • Signal-to-noise • Cross-axis sensitivity • Temperature stability • Switching time • Contact force • Efficiency (Q) • Power transmission • Process corners • Opens & shorts • Release etching • CVD, sputtering,… • RIE, wet etch,… • And more…
Simulate
The Traditional Approach to MEMS Design
© Coventor Inc. 2013 Slide 6
ASIC Design
MEMS Design
Fab / Foundry
MEMS Process Learning Cycle
MEMS Process Learning Cycle
MEMS Process Learning Cycle
Control System Design Control System Design Control System Design
Conventional FEA
Conventional FEA Conventional FEA Conventional
Modeling Modeling Modeling Modeling
IC Design IC Design IC Design
Over-simplified, non-parametric
Too slow to inform fab cycles Full coupling infeasible
Hand-crafted
Design-specific
Consequence: too many “build and test” cycles
MEMS+ The New Approach
© Coventor Inc. 2012 Slide 7
MEMS+ Simulator
MATLAB
Simulink
Virtuoso
Simulate and Analyze Enter Design in 3D Visualize Results in 3D
MEMS+ Finite Element Library: MEMS-specific, 3D, high-order, parametric
A tool for creating compact finite element models that run in MATLAB, Simulink, and Cadence
MEMS+ a different kind of FEA
Traditional Finite Element Analysis
3D Geometry
Mesh Generator
Library of generic, low-order
finite elements
Brick, tet, shell, and beam elements
Meshed Model
Large 10k to 10M DoF
MEMS+ Finite Element Analysis
3D Design Entry in Graphical UI
Library of parametric, MEMS-specific, high-order finite elements
Scripting in MATLAB or Python
or
Meshed Model
Small 10 to 1000 DoF
Overview of the MEMS+ Element Library
Rigid Shapes Flexible Shapes Beams Suspensions Start with Mechanical Components
In-Plane Electrodes
Side Electrodes
Interdigitated Combs
Piezo Layers Add Electro-
Mechanical Coupling
Squeezed-Film Damping
Fluid Chambers
Pressure Loads Add Fluid
Damping and Loading
MEMS+ Application Examples
Slide 10
DLP mirror, 11 DoF
RF Switch 119 DoF
Gyroscope, 96 DoF Accelerometer, 67 DoF Ring Gyro, 345 DoF
Ring Resonator, 727 DoF
MEMS+ is general. MEMS+ models are small, but accurate and simulate fast for rapid design and manufacturability studies
Why use MEMS+
MEMS present specific simulation challenges
© Coventor Inc. 2012 Slide 11
MEMS are multi-physics Mechanics + electrostatics + fluidic effects + packaging effects + etc.
MEMS are part of a system • MEMS + control system • MEMS + IC
MEMS+ can simulate fully coupled physics
• Dynamic response • Rapid design studies • Design optimization • Manfacturability
MEMS+ models work in system and IC tools
• Closed-loop operation • Noise analysis • Device arrays
Case Study: MEMS Varactor Manufacturability
Recent Successes, Designed with Coventor…
© Coventor Inc. 2012 Slide 13
“Thank you for developing MEMS tools that support our needs for composite piezo materials”
– Harmeet Bhugra, Managing Director, MEMS Product Line
The first piezo MEMS timing solution, announced in 2011
TDCA, the first RF MEMS varactor array to ship in cell phones, Samsung phone tear down, 2011
MEMS Varactor Modeling Methodology
© Coventor Inc. 2011 Slide 14
Deformation vs. bias voltage
Quasi-static pull-in analysis in MEMS+ and CoventorWare
Simulated in MEMS+
2. Verification of MEMS+ model with conventional FEA Deformation due to process-induced stress gradient
Simulated in MEMS+ and CoventorWare
Disclaimer: Design shown is from an EU project, NOT from WiSpry or another customer
Design entered in MEMS+
1. Parametric design entered in MEMS+ intuitive UI
Varactor Array Capacitance
© Coventor Inc. 2011 Slide 15
0 10 20 30 40
Tota
l Arr
ay
Capa
cita
nce
Bias Voltage
Array 1Array 2Array 3Array 4Array 5
Designed pull-in V
Supplied measured data (mock up of proprietary info) • Each array has 100s of varactors • Multiple arrays measured from different wafer locations
Huge variation in pull-in voltage is caused by process variations
Process Variation Assumptions
Slide 16
Parameter Nominal Delta
Mech1 Mean Stress (Mpa) 60 ± 100%
Mech1 Delta Stress (Mpa) 80 ± 90%
Mech2 Stress (Mpa) -170 ± 35%
Mech1 Thickness (um) 0.2 ± 10%
Varactor Gap (um) 1.0 ± 5%
mech1
mech2
mean residual stress and stress gradient
gap thickness
Which process variations cause the large variation in pull-in voltage?
Process cross section
Multi-variable sensitivity analysis
Coventor Inc. Confidential Slide 17
5-way virtual experiment on a parametric MEMS+ model, scripted in MATLAB
Pull-In Sensitivity Simulated in MEMS+
Slide 18
Mech1 Mean Residual Stress (Mpa) Mech2 Residual Stress (Mpa) Gap (um)
Pull_
in (V
)
24
22
20
18
16
14
12 -10 20 50 80 110 -245 -215 -185 -155 -125 0.71 0.73 0.75 0.77 0.79
thickness mech1
mech2
mean residual stress
gap
Total Variation Analysis
Slide 19
Use the variation envelope to predict yield Example: Tolerance of ±4V from nominal pull-in voltage gives 55% yield
Total Variation = Root Sum Squares ( input variations normalized by SD )
Polysilicon thickness Young’s Modulus variation Y-mode Frequency Z-mode Frequency
MEMS+ models enable manufacturability studies
+ MATLAB script
10 minutes CPU time to compute 400 mode frequencies
MEMS+ model
Example: Modal frequencies vs. cross-wafer non-uniformity
Import to Cadence for transient analysis & IC design
Slide 21 Exposed parameters of interest
Exposed pins of interest
Virtual Fabrication with SEMulator3D
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Detailed Process Description
Metal 1
Metal 2
Metal 3
Metal 4
Metal 5
Si3N4
Substrate
SiGe BiCMOS Process (HBTs, MOSFETs)
High-Voltage Electrodes for electrostatic actuation
RF-Signal Line
Met
alliz
atio
n of
BiC
MO
S
RFMEMS Switch is embedded in to metallization levels of BiCMOS process
Suspended Membrane (Metal3)
2D Design Data (GDS2 Layout)
Proven Value • Process Development • Design Verification
Silicon-Accurate 3D Models
2D Cross Sections
Conclusion: MEMS+ is a New Approach
© Coventor Inc. 2013 Slide 24
ASIC Design
MEMS Design
Fab / Foundry
MEMS Process Learning Cycle
MEMS Process Learning Cycle
Control System Design
Conventional FEA
Modeling
IC Design
Complementary, for details and verifying MEMS+
Automatically generated, parametric, tunable accuracy vs. speed
Industrial strength, Fast AND Accurate, Full coupling feasible
Result: fewer “build and test” cycles
MEMS+, A Different Kind of FEA Rapid Design Studies Optimization Manufacturability
Discussion
