the art of mems+ic simulation - semicon taiwanparameterized mems component library (.lib) coventor...
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The Art of MEMS+IC Simulation
MEMS+ 2.0: Enabling System-level Design with Matlab, Simulink and Cadence Virtuoso
The Art of MEMS+IC Simulation
MEMS+ 2.0: Enabling System-level Design with Matlab, Simulink and Cadence Virtuoso
Angela Chao, PhD / 趙月秀 博士Technical Manager / 技術經理
www.apic.com.tw
SEMICON Taiwan, September 2011
Angela Chao, PhD / 趙月秀 博士Technical Manager / 技術經理
www.apic.com.tw
SEMICON Taiwan, September 2011
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• MEMS are micro‐ or nano‐scaled devices
• Typically comprise a MEMS sensing or actuation device and integrated electronics
• Disconnect between MEMS and IC design flows leads to long development cycles and high costs
• Minimal design reuse
Introduction
Digital micro-mirror device (DMD)by Texas Instruments
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• IC and layout designers require a MEMS component for their IC design environment
MEMS Product Design Requires Collaboration
IC Design and Simulation ToolsMEMS Design and Simulation Tools
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• How can an accurate circuit or system model be created considering the complexity of state‐of‐the‐art MEMS devices?
The Collaboration Challenge
Analog Devices, Inc. All rights reserved
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• Reduced Order Modeling yields a system or circuit model starting with a classic FE element model:
Reduced Order Modeling
+ Flexible approach, only limited by what can be modeled with FEA
– Non‐parametric– Hard to include mechanical nonlinearities and contact models
– Time consuming/hard to automate
– Requires in‐depth FEA knowledge
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Requests leading MEMS manufacturers for parametric models
• “Every time my MEMS team changes the device geometry, they not onlyhave to re‐extract, but also re‐validate the model, which limits our ability to quickly co‐design with our circuit team”
• “It’s important to give the circuit team a few geometric parameters to vary so they can optimize the system characteristics.”
• “To improve yield of the entire system, we need the entire model to be sensitive to manufacturing variations in the geometry.”
Why parametric models are needed
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• Circuit simulator compatible lumped models of non‐electrical components such as plates, beams, electrodes etc:
+ Parametric, enabling yield, parameter and Monte Carlo studies
+ Can handle most forms of nonlinearities– Flexibility and applicability depends on the quality of the available model writing skills or existing component libraries
Behavioral Modeling Approach
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• Our first answer: CoventorWare Architect, a schematic based approach to MEMS+IC/System simulation:
CoventorWare Architect
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• Every schematic model had a rich set of parameters in order to enable a maximum of design flexibility:
Schematic Model Parameterization
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• Schematic creation was often perceived as laborious and non‐intuitive…
• Scene3D brought some relief
3D Model with Scene3D
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• Users were often impressed by the simulation speed but had a hard time to appreciate the complexity of Architect simulations…
Simulation Speed
More the 10000 time steps in only 7min on a standard laptop!
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…so we added 3D result visualization…
The animation is greatly exaggerated in vertical direction
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• With continuing improvements to our component library, ARCHITECT could handle an increasing variety of designs…
• …and Architect was no longer just about MEMS+IC design. Full MEMS device design could be done in minutes
Architect Examples
DLP Mirrors Ring Gyros
RF SwitchesResonators
Accelerometer
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• Schematic based model creation was still unnatural for most mechanical engineers who prefer CAD tools or at least layout editors for design input
• Most IC and system designers prefer MATLAB Simulink, Cadence, Mentor Graphics, Synopsys (rather than SABER!)
• Our most valuable asset, our model librarywas trapped inside SABER …
Remaining Caveats
> 15 Man Years
Saber -Mast
Behavioral Model Libraryin C++
> 15 Years
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Our New Approach MEMS+
FEM Damping and Stress Analysis
Algorithm Level Design
Structural Level Design and PCell Generation
SEMulator3D
Process Emulation
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Insert MEMS model in schematic3
Parameterized MEMS Component Library (.lib)
Coventor MEMS+
Assemble design in 3‐D1
Visualize simulations in 3‐D5
Coventor MEMS+for Matlab Simulink
S‐Function Interface
Simulate4
Import MEMS Model 2
Symbol
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Parameterized MEMS Component Library (.lib)
Coventor MEMS+
Assemble design in 3‐D1
Coventor MEMS+ for Cadence Virtuoso
Visualize simulations in 3‐D6
Import MEMS Model 2
P‐Cell
Netlist
Symbol
Cadence VirtuosoInsert MEMS model in schematic
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Place MEMS pCell in layout5
Spectre/UltraSim
Simulate4
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MEMS+ PDK and 3D design entry
3D MEMS+model based on Analog Devices ADXL202 design data available to the public
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• All foundry relevant data is stored in two databases, which are either provided by an external foundry or by the technology group within the company
Foundry Data PDK
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• Material properties can be defined as values, variables or algebraic equations
Variable Assignment
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• The Process Editor details the sequence of MEMS fabrication steps
• It holds layer names, thicknesses and sidewall angles
Process Editor
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• Each layer is associated to one of the materials from the Material Database
Layer Material Selection
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• Variables defined in the Material Database or Process Editor can be exposed to the MEMS designer
Exposing Variables
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• The MEMS designer starts with a blank, 3‐D canvas on the Innovator tab
Innovator
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• Exposed variables from the Process Editor or Material Database are automatically imported into Innovator
PDK Variable Import
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• MEMS device models are created with a library of parametric component generators for suspensions, plates, combs and electrical pads
Parametric Component Library
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• The MEMS designer picks components from the library to assemble the desired structure
Adding Components
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• Each component can be assigned to one or multiple layers of the corresponding process file
Layer Assignment
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• Component parameters can be defined as values, variables or algebraic equations
Component Parameters
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• The component tree highlights the component names and the hierarchical structure of the 3‐D device schematic
Component Tree
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• The mechanical connector tree and viewing mode highlights which components are linked together
Mechanical Connector View
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• The electrical viewing mode highlights electrical connectivity with colors and transparency in the canvas
Electrical Connector View
Only electrical layers are shown as solid
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• 3D Innovator designs can be imported into Matlab Simulink’s model editor using the MEMS+ import tool
Matlab Simulink Model Import
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• The MEMS device model in Matlab Simulink features all parameters that were exposed in MEMS+ Innovator
Model Parameters
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• The symbol view features all exposed electrical, mechanical and capacitance ports
Exposed Ports
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• Exposed electrical ports appear as voltage inputs
• Exposed mechanical ports appear as force/torque inputs and position/angle variation outputs
• Exposed capacitance ports are pure outputs
Input/Output Ports
VoltageInputs
ReferenceFrame motionInputs
Capacitance Outputs
PositionOutputs
ForceInputs
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• The MEMS system designer completes the feedback or post processing circuit using models from the standard library
System Schematic
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• The MEMS system designer confirms the device performance runningsimulations in the Matlab/Simulink environment
MEMS Device Simulation
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• Additional analysis are accessible from the MEMS+ menu…
Additionally Supported Analysis
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• The DC Analysis is a convenient way to create operating points for transient and frequency analysis
DC Analysis
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• The Modal Analysis calculates Eigenmodes and Eigen‐frequencies of the complete system
Modal Analysis
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• The AC Analysis performs frequency sweeps of the complete system
AC Small‐Signal Analysis
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• All simulation results can be loaded back into MEMS+ and animated in the 3‐D canvas
Simulation Results
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Parameterized MEMS Component Library (.lib)
Coventor MEMS+
Assemble design in 3‐D1
MEMS+ Workflowfor Cadence Virtuoso
Visualize simulations in 3‐D6
Import MEMS Model 2
P‐Cell
Netlist
Symbol
Cadence VirtuosoInsert MEMS model in schematic
3
Place MEMS pCell in layout5
Spectre/UltraSim
Simulate4
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• Texas Instrument’s digital light processing [DLP] projection system is build around a digital micro‐mirror device (DMD) on top of a SRAM cell
DLP Mirror Design Example
DLP mirror with memory cell
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DLP mirror in MEMS+2
Memory cell schematic 3
Schematic of the combined device and memory cell model
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Hierarchical symbol of a DLP mirror with memory cell
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• The position and orientation of the DLP mirror is part of the exposed variables
Complete Device Design
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• The 3D Innovator design is imported into the Cadence Library Manager using the MEMS+ import tool
Cadence Virtuoso Cell Generation
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• The MEMS+ import tool automatically creates a parametric layout and schematic view
Parametric Cell Views
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• The created cell views features all parameters that were exposed in MEMS+
Virtuoso Cell Parameters
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• The MEMS designer adds sources to the exposed electrical pins and confirms the device performance running DC, AC and transient simulations
MEMS Device Schematic
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• Simulation results can be loaded back into MEMS+ and animated in the 3‐D canvas
MEMS Device Simulation
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• The IC designer, meanwhile, creates a schematic of the SRAM memory cell underneath each mirror…
SRAM Memory Cell Design
Bit Line ~Bit Line
Word Line
Bit Line ~Bit Line
Data ~Data Data ~Data
Word Line
Cadence Virtuoso schematic of the memory cell
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• The CMOS SRAM cell can in turn be connected to the mirror to assemble the complete pixel cell
Complete Pixel Cell
DLP mirror with memory cell
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DLP mirror in MEMS+2
Memory cell schematic 3
Schematic of the combined device and memory cell model
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Hierarchical symbol of a DLP mirror with memory cell
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• The pixel cell is replicated to form an array and connected to the driving electronics
Mirror Array Schematic
Hierarchical symbol of a DLP mirror with memory cell
Cadence Virtuoso schematic of memory cell
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• The complete mirror array can now be simulated with the Virtuososimulators: Spectre, UltraSim or APS
Mirror Array Simulation
150s in less then 30min real time!
Visualization in MEMS+ Scene3D
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• MEMS+ takes full advantage of the Cadence Virtuoso custom IC design environment
Integration
Monte‐Carloand Yield Analysis
ParasiticCapacitanceExtraction
CombinedDRC
SignoffMEMS‐ICSimulation
Parametric MEMS+ Design
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MEMS+Design ExamplesMEMS+MEMS+Design ExamplesDesign Examples
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Lamé‐Mode Resonator
MEMS+model build with one 4th order rectangular plate and four beams
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• Band‐pass filter can be build by combining multiple Lamé resonators:
Lamé‐Mode Filter
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• Microphone with perforated back plate using circular and arc shaped flexible plates with pressure loads and electrodes
Microphone
(Perforation are not shown in the image) Results of a Modal Analysis with Matlab/Simulink
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• Mirror with circular pze membrane actuation:
PZE Actuated Mirror
Vertical Mirror displacement [um] as a function of voltage
QuadrilateralPlates with Piezo Layer
Rigid Cylinder(Mirror)
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• Disk Gyroscope build with pie and arc shaped flexible plate models with side and top electrodes
Disk Gyro
Vertical Beam
Pie Plates Arc Plates with Side and Top Electrodes
MEMS+ mode shapes compared to a traditional parabolic brick mesh
1.22MHz 7.53MHz7.53MHz1.23MHz
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• MEMS+ ring resonator made with straight beams, arc plates and side electrodes
Ring Resonator
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• MEMS+ generated accelerometer model with SD force feedback loop in Cadence Spectre:
Accelerometerwith ΣΔ Feedback Loop
The transient simulation with Spectrecompleted in less then 10 seconds !
Acceleration Input
Plate Displacement
Control Signal
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• MEMS+ builds on Coventor’s parametric model library which has been proven on real‐world designs…
MEMS+Design Examples
Display Devices
RF Switches
Resonators
Gyros (Angular Rate Sensors)Accelerometers
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The End
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