Transient Temperature Analysis. Rajit Chandra, Ph.D. Gradient Design Automation

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1 Transient Temperature Analysis Rajit Chandra, Ph.D. Gradient Design Automation

2 Trends in mixed signal designs More designs with switching high power drivers (smart power chips, automotive, high-speed communications, ) Switching power sources affect device, and die temperatures Reliable power drive requirements for safety critical applications Trends in integration analog, digital, systems-in- package, dense power distribution!!!! Slow time-varying power source performance affected by transient temperatures that steady state analysis cannot detect Max device temperature can exceed spec momentarily causing permanent damage High temperature can momentarily reduce power drive causing malfunction Transitory failure conditions caused by higher temperature distributions 2

3 Steady state versus transient analysis " Steady state temperature analysis based on average power " Faster digital switching power sources affected not by instantaneous but by average temperatures " Transition time of power transistors compare with rate of temperature response of die " Electrical response is affected by instantaneous temperatures, causing possible malfunctions Effect of transient temperature across die PTAT response T PTAT response with transient temperatures Expected response with uniform temperature Instance temperature based response Temperature at PTAT

4 Motivation for full chip transient thermal analysis: " Duty cycle of power sources affect rate of heat dissipation " Several thermal time constants are involved for example: " Individual device temperatures peak ~ 100 s of us " Die temperatures ~ ms " Package and substrate ~ seconds " Accumulated heat can cause instantaneous peak junction temperature to be much higher than steady state values " Temperatures can exceed spec for devices " Cause problems with circuit performance, reliability, burn out Max Power, Temperature ON OFF Junction temperature! Period Time 4

5 Effects of temperature transients Device self-heating Joule (interconnect heating) Temperature difference across circuits Duty cycle of instance power waveform!!!! Performance degradation and malfunctions Electromigration and reliability Parametric failures Peak instantaneous temperatures surpassing tolerance thresholds Device response time comparable to temperature time constant! Deviation from expected electrical behavior of device e.g: signal timing, power drive, signal wave shape 5

6 Challenges of transient thermal analysis " Existing transient temperature analysis methods: " Fully coupled electrical and thermal simulation " Long run times, does not scale to full chip analysis, closely tied with circuit simulator " Relaxation methods with separate but synchronized thermal and electrical simulation " Accurate, scaleable in performance, can be integrated with multiple circuit simulators " Allows mixed level circuit descriptions, handles digital blocks, transistor circuits and architectural evaluations prior to final layout " For present day design complexity fully coupled analysis tools are too slow and restrictive relaxation method is a better choice 6

7 Requirements for full chip transient analysis " Compute and track rates of temperature changes within die " Determine critical time interval for temperature evaluation " Update instance temperatures based on self & heat coupling " Update instance power with temperature change " Model time varying waveform for power sources " Detect temperature limits specified by users " Manage and synchronize transient electro-thermal thermal simulation 7

8 Support finefine-grain analysis for accuracy of hotspot magnitude and location Coarse-grain Fine-grain 8

9 Example testcase " Based on a customer donated design: " 3 x 4 mm die with power transistor & PTAT circuit " 0.35u technology node " 0.6mm X 0.7mm power sources " 3 metal layers, pad layer " Power: Trapezoidal pulse train, rise and fall time:0.1mm, width: 1ms, period:5ms, max power:22w " This example demonstrates: -Transient temperature analysis -Times at which power source reaches specified temperatures -Transitory temperature effect 9

10 Snapshots of temperature profile of power source 10

11 Transient temperature analysis flow Technology File Time Varying Power Sources Design Layout Power Sources CircuitFire Transient Temperature Analysis Instance Power Circuit simulator Package Model Temperature Specs Report: Temperature Specification Violations Instance temperatures at critical time intervals Event synchronizer Netlist with temperatures control file device models 11

12 Technology features " High capacity, high resolution " Incorporates package and boundary conditions " True 3-D temperature analysis "Detail temperature for all design objects on all layers " Comprehensive data visualization " Interoperability with current tools & flows 12

13 Control parameters and output data " Control file allows runtime/accuracy tradeoff " Parameters to define accuracy " Parameters for adaptive grid based on "Output: "Power source geometries, thermal and power gradients "Temperature within die: 3D visualization with archives "Temperate & power per instance "Temperature & power per wire shape 13

14 User defined analysis features " Set max limit of instance temperature " Set max temperature difference between instances " Save and run from specified state and time " Query time stamp of instance temperatures " Warning and error reports for specified limits " User definable "Waveform viewer plug-ins "Temperature archives for detailed analysis 14

15 Use models: " Batch mode " Command file, input data files, archived data useful for examining with interactive graphics for large designs " Interactive mode (Tcl based) " Define power source parameters, change locations rotation " Redefine power waveform or temperaturepower lookup " Evaluate material thermal parameters and package parameters " Interactive mode is ideal for design exploration! 15

16 Ambient temperatures can be harsh need to consider detailed package models 16

17 Accuracy of package models: CircuitFire-Flomerics Flomerics interface - a bridge between package and design worlds " Accuracy of package thermal prediction can be improved by coupling 3-D package simulation with FireBolt " Allows inclusion of complex cooling mechanism Packaging Die thermal profile Design Flomerics CircuitFire Design Package model Layout 17

18 Takes package and ambient into account Air flow 18

19 Validation of Results " Measurement on silicon with thermal diode and different package models Test Case Power (W) θja (K/W) Measured Tj ( C) measured using diode GDA s Tj ( C) average diode temperature Epad Epad Slug Slug " Measurement on silicon with PTAT circuit: Thermal analysis results annotated into Spice simulator and validated with lab measurements " Correlation with infra red camera and GUI temperature distribution 19

20 Summary " Mixed signal designs use power devices for commercial and industrial use " Higher levels of device integration and power densities cause steep temperature variations in many applications " Transitory temperature profiles can cause performance and reliability issues, or even permanent device failure " CircuitFire provides a full chip level solution with package parameters that can be integrated with circuit simulators and layout editors 20