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Global Modeling of High Frequency Circuits and Devices

Global Modeling of High Frequency Circuits and Devices. Committee chairman: Dr. M. Saraniti, (ECE, IIT) Committee members: Dr. T.Y. Wong, (ECE, IIT) Dr. A.Z. Wang, (ECE, IIT) Dr. C.U. Segre, (BCPS, IIT) Dr. D.K. Ferry, (EE, ASU). PhD defense by Julien Branlard.

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Global Modeling of High Frequency Circuits and Devices

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  1. Global Modeling of High Frequency Circuits and Devices Committee chairman: Dr. M. Saraniti, (ECE, IIT) Committee members: Dr. T.Y. Wong, (ECE, IIT) Dr. A.Z. Wang, (ECE, IIT) Dr. C.U. Segre, (BCPS, IIT) Dr. D.K. Ferry, (EE, ASU) PhD defense by Julien Branlard Chicago, November 19th 2004

  2. INTRODUCTION 1 1- Presentation outline • The simulation tool • GaAs devices • Small-signal analysis • Noise analysis • Memory management • Conclusions Chicago, November 19th, 2004

  3. INTRODUCTION 1 2- Full-band particle-based simulations • Full-band model • Cellular Monte Carlo (CMC) GaAs Chicago, November 19th, 2004

  4. INTRODUCTION 1 2- Full-band particle-based simulations • Full-band model • Cellular Monte Carlo (CMC) • Scattering • phonon,impurity,impact ionization Chicago, November 19th, 2004

  5. INTRODUCTION 1 2- Full-band particle-based simulations • Full-band model • Cellular Monte Carlo (CMC) • Scattering • phonon,impurity,impact ionization • Bulk simulations • very good agreement with published data Chicago, November 19th, 2004

  6. INTRODUCTION 1 3- Ensemble* and Cellular◊ Monte Carlo scattering carrier (e,k) (e’,k’) CMC EMC • Pre-compute all possible final energies and momenta • Associate a probability • Store these rates in look up tables • Compute the new energy and momentum during run-time * M.V. Fischetti and S.E. Laux, “MC analysis of electron transport in small semiconductor devices” ◊ M. Saraniti and S.M. Goodnick, “Hybrid Fullband Cellular Automaton/ Monte Carlo Approach for Fast Simulation of Charge Transport in Semiconductor” Chicago, November 19th, 2004

  7. S G D ND+ N GaAs DEVICES 2 1- GaAs MESFETs: geometry • Structural simplicity • “High speed”, low noise applications D S G Chicago, November 19th, 2004

  8. GaAs DEVICES 2 2- GaAs MESFETs: DC characteristics • Gate length and width: LG , WG • Doping profile: ND+ , N • Operating point: VDS , VGS Chicago, November 19th, 2004

  9. LG S S D D WG WG n+ n+ n n LG WG WG GaAs DEVICES 2 3- GaAs MESFETs: 3D devices • Various geometry: LG , WG • 2D / 3D characterization G G Chicago, November 19th, 2004

  10. G S D d ND substrate GaAs DEVICES 2 4- GaAs MESFETs: Gunn oscillations • Gunn domain d =1300 nm ND=1017 cm-3 fosc = 50 GHz d =650 nm ND=2x1017 cm-3 fosc = 100 GHz Chicago, November 19th, 2004

  11. VGS < 0 VDS > 0 DRAIN GATE SOURCE AlGaAs n+ spacer GaAs n 2DEG GaAs DEVICES 2 5- AlGaAs/GaAs HEMTs: geometry Chicago, November 19th, 2004

  12. GaAs DEVICES 2 6- AlGaAs/GaAs HEMTs: DC characteristics Chicago, November 19th, 2004

  13. v(t) i(t) ΔV G D VG v(t) 0 T S i(t) 0 T Frequency Analysis 3 1- Problem definition: • STEP 1: Apply a voltage perturbation on one electrode • STEP 2: Compute the Fourier transform • STEP 3: Compute the complex impedance and gains Chicago, November 19th, 2004

  14. DVGS DVDS Frequency Analysis 3 1- Problem definition: figures-of-merit for constant VGS for constant VDS Chicago, November 19th, 2004

  15. Frequency Analysis 3 1- Problem definition: Y-parameters Chicago, November 19th, 2004

  16. Frequency Analysis 3 2- Sinusoidal excitation: • Apply a sinusoidal voltage on one electrode Simulation time: T Frequency of interest ISS Chicago, November 19th, 2004

  17. fXm 50 GHz Frequency Analysis 3 2- Sinusoidal excitation: • Compute the complex output impedance LG = 100 nm Chicago, November 19th, 2004

  18. Frequency Analysis 3 2- Sinusoidal excitation • How many periods to apply ? Chicago, November 19th, 2004

  19. ΔV 0 T Frequency Analysis 3 3- Fourier decomposition* Simulation time: T Frequency resolution: Maximum reachable frequency: Sampling time step: DT * R.W. Hockney, and J.W. Eastwood: Computer Simulation Using Particles, 1988 Chicago, November 19th, 2004

  20. fT 60 GHz ~ fXm 60 GHz ~ Frequency Analysis 3 3- Fourier decomposition • Compute the complex output impedance LG = 98 nm Chicago, November 19th, 2004

  21. Frequency Analysis 3 4- Polychromatic sinusoids • Apply a sum of sinusoids voltage on one electrode Simulation time: T Frequency of interest Harmonics: for Chicago, November 19th, 2004

  22. Frequency Analysis 3 4- Polychromatic sinusoids • Importance of the operating point VGS , VDS Chicago, November 19th, 2004

  23. Frequency Analysis 3 4- Polychromatic sinusoids • Compute the complex output impedance for LG = 100 nm Chicago, November 19th, 2004

  24. Frequency Analysis 3 5- Approach comparison • Fourier Decomposition frequency spectrum long simulation time • Sinusoidal Excitation • more flexible • more precise fXm = 50 GHz Chicago, November 19th, 2004

  25. Frequency Analysis 3 6- Perturbation on the gate: derive gains • Output voltage gain: MESFET LG = 100 nm Chicago, November 19th, 2004

  26. Frequency Analysis 3 6- Perturbation on the gate: derive gains • Short circuit current gain: MESFET HEMT fT = 125 GHz fT = 70 GHz LG = 100 nm LG = 100 nm Chicago, November 19th, 2004

  27. Frequency Analysis 3 6- Perturbation on the gate: derive gains • Comparison with published data * * F. Schwierz, J.J. Liou, “ Modern Microwave transistors”, 2003 Chicago, November 19th, 2004

  28. Frequency Analysis 3 6- Perturbation on the gate: derive gains • Unilateral Power Gain (UPG) MESFET LG=100 nm Chicago, November 19th, 2004

  29. Noise Analysis 4 1- Two modes of analysis • Device maintained in steady state: Iss Vss • Current noise modecurrent fluctuations • Autocorrelation function • Power spectral density • Voltage noise modevoltage fluctuations • Autocorrelation function • Power spectral density Chicago, November 19th, 2004

  30. Noise Analysis 4 2- Spectrum analysis • Biased autocorrelation • Correlogram Chicago, November 19th, 2004

  31. Noise Analysis 4 3- Current Noise • Autocorrelation function • exponential decay • plasma relaxation time • dielectric relaxation time AlGaAs/GaAs HEMT Chicago, November 19th, 2004

  32. fp (n) fp (n+) Noise Analysis 4 3- Current Noise • Density spectrum • plasma oscillation AlGaAs/GaAs HEMT Chicago, November 19th, 2004

  33. Noise Analysis 4 3- Current Noise • Spectral Densities: low frequency • shot noiselinear behaviorcarriers in the depletion region • thermal noisespatially distributed independent of applied voltage • excess noisehot carriers close to the drain electrode shot thermal excess applied bias [mV] GaAs n+n diode Chicago, November 19th, 2004

  34. Noise Analysis 4 4- Voltage Noise • Autocorrelation function • oscillationsplasma relaxation time dielectric relaxation time • higher voltages GaAs n+n diode Chicago, November 19th, 2004

  35. Noise Analysis 4 4- Voltage Noise • Spectral Density GaAs n+n diode Chicago, November 19th, 2004

  36. Noise Analysis 4 4- Voltage Noise • Spectral Density GaAs n+n diode Chicago, November 19th, 2004

  37. 2DEG AlGaAs n+ Noise Analysis 4 4- Voltage Noise • Spectral Density: HEMT GATE SOURCE Chicago, November 19th, 2004

  38. Noise Analysis 4 4- Voltage Noise • Spectral Density Derivative • shot noisedominant for low voltages • thermal noise spatially distributed • excess noisehot carriers near end of the device shot excess thermal GaAs n+n diode Chicago, November 19th, 2004

  39. CMC Memory Usage 5 1- CMC Scattering: problem definition • Scattering Tables 4 Bytes address rate Total size: 8 Bytes Significant digits: 7 Chicago, November 19th, 2004

  40. CMC Memory Usage 5 2- First approach: 25% savings • Principle 4 Bytes • Lesser precision excellent agreement on all materials • Memory misalignmentcompiler dependent slower execution overcome by faster arithmetic address rate rate Total size: 6 Bytes Significant digits: 4 Chicago, November 19th, 2004

  41. CMC Memory Usage 5 2- First approach: 25% savings • Bulk simulations • Tested on GaAs, Si, Ge, GaN (wurtzite and zincblende) • Excellent agreement • 25% reduction achieved Chicago, November 19th, 2004

  42. CMC Memory Usage 5 3- Second approach: 50% savings • Principle • Addressing absolute relative • Use of offsets phonon scattering < impact ionization • Normalizing the rates rmax • Joining the rate and the address 4 Bytes address address distance rate rate Total size: 4 Bytes Significant digits: dynamic Chicago, November 19th, 2004

  43. CMC Memory Usage 5 3- Second approach: 50% savings • Bulk simulations • Tested on GaAs, Si, Ge, GaN (wurtzite and zincblende) • Excellent agreement • 50% reduction achieved Chicago, November 19th, 2004

  44. CMC Memory Usage 5 3- Second approach: 50% savings • Error estimation Chicago, November 19th, 2004

  45. CMC Memory Usage 5 3- Second approach: 50% savings • Performance Chicago, November 19th, 2004

  46. Summary 6 • 2D and 3D simulations of GaAs devices diodes, MESFETs, HEMTs • Small-signal analysis Investigated several methods Implemented a hybrid approach Derived full small-signal parameters • Noise analysis Investigated current and voltage noise approach Studied GaAs devices Identified frequency behavior Voltage dependence Spatial distribution • Memory management Implemented two algorithmic optimizations Achieved the requested compression Gain in computational efficiency New horizons for the CMC Chicago, November 19th, 2004

  47. Thank You ! Chicago, November 19th, 2004

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