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PUT JOSH WEB-STREAM HERE. 4/30/2010 Iowa State University EE492 – Senior Design II. IRP Review: A TEST CHIP FOR ELECTROMIGRATION STUDIES Karl Peterson (EE), Emmanuel Owusu ( CprE ), and Joshua Ellis (EE). Our project is special…. International collaboration - PowerPoint PPT Presentation
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PUT JOSH WEB-STREAM HERE
IRP Review:A TEST CHIP FOR ELECTROMIGRATION STUDIESKarl Peterson (EE), Emmanuel Owusu (CprE), and Joshua Ellis (EE)
4/30/2010Iowa State UniversityEE492 – Senior Design II
Our project is special…
International collaboration
Product conceptualization & specification in addition to design
Integrated circuit (IC) rather than system design
Research-orientated objectives
Problem Statement Design a test chip to support
ISU research on electromigration & IC reliability
The chip must include test structures composed of actual metal interconnects in a modern silicon process
Must be capable of interfacing with a controller to allow electrothermal conditions in the chip to be varied and monitored.
The Big Picture Electromigration – a complex
physical phenomena that causes mechanical stress in metal interconnects
Important failure mechanism in ICs
Strong, non-linear dependence on current-density and temperature
Need models for electromigration that predict reliability under practical conditions
Electromigration in progress!
Electromigration testing Subject interconnects to
variable electrothermal stresses
Measure time-to-failure of many samples
Analyze statistics, develop models, fit data, etc.
Use accelerated lifetime technique
Very high temperatures and current densities!
Proposed Solution Proposed IC contains 8 identical
metal test structures Current-steering Digital-to-
Analog Converter provides 0-25mA to test structure
On-die analog temperature sensing circuits
Open-circuit detection Control logic with serial interface Process technology:
0.18 µm standard CMOS
System Diagram
DAC #2 DAC #3 DAC #4DAC #1
Test Structure
#1
Test Structure
#2
Test Structure
#3
Test Structure
#4
I<2>
Open-Circuit Detect
Open-Circuit Detect
Open-Circuit Detect
Open-Circuit Detect
I<3> I<4>I<1>
FAIL<1> FAIL<2> FAIL<3> FAIL<4>
Control Logic
...
I_EN
GND
VDD
I_WR_ENI_DATAADDR_WR_ENADDR_DATAFAIL
Temperature Sensor
Temperature Sensor
Temperature Sensor...
TEMP_1
TEMP_2
TEMP_3
Test Structure Single-layer metal
interconnect with serpentine pattern
Metal layer M1Width 0.23 µm
Equivalent length
Up to 11.5 mm
Thickness 210 nm
Material Cu
Test structure – detail Corners reinforced
to mitigate current crowding
Current-Steering DAC
Current range of 0 to 25 mA
7 bit resolution LSB Current – 200 µA Current-Steering
Architecture Binary-weighted sources Constant power
Open Circuit Detection Two inverters on the output
DAC0010110
Current-Steering DAC
Temperature sensor
Compact, CMOS-based sensor design
5 sensor distributed throughout the floor plan
Control Logic Serial interface Simple
protocol Low pin-count
Digital flow
Needed standard cell library for synthesis
Free, scalable library did not meet design rules of our process
Extensive work to customize , re-verify standard cells
Auxiliary blocks
Master current switch Reference-distribution
network
Physical Design Floorplan symmetry
to prevent uncontrolled experimental variables
Significant redundancy and reinforcement of non-test blocks for reliability
Final design is 860 µm x 860 µm
Top-Level Layout
Simulations & Verification Analog verification: relevant
performance parameters for each block tested over full PVT range with 500-run statistical simulations
Digital verification: functional simulations, timing analysis
System-level, mixed-signal verification: several long transient simulations covering typical operation sequence
Top-level Functional Simulation
#1 VDD rises
#2 Reference current starts
#3 <000> written to address reg.
#4 <0101010> written to address reg.
#5 master current switch enabled
#6 test current settles at predicted value
Questions? Comments?
Backup slides – test results DAC Temperature sensor Top-level functional
DAC Simulation Results
Temperature sensor – supply sensitivity, nominal design
Temperature Sensor – Stat. Sim.
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