Self-heating investigation of bulk and SOI transistors - PowerPoint PPT Presentation

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Self-heating investigation of bulk and SOI transistors

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Pierre-Yvan Sulima, H l ne Beckrich, Jean Luc Battaglia, Thomas Zimmer. University of Bordeaux 1, France. ST Microelectronics. April 8, 2005. MOS-AK, Strasbourg ... – PowerPoint PPT presentation

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Title: Self-heating investigation of bulk and SOI transistors


1
Self-heating investigation of bulk and SOI
transistors
  • Pierre-Yvan Sulima, Hélène Beckrich, Jean Luc
    Battaglia, Thomas Zimmer
  • University of Bordeaux 1, France
  • ST Microelectronics

2
Preface
  • This presentation deals
  • with bipolar transistors
  • with heat transfer
  • but
  • Heat transfer is material dependant
  • MOS BJT gt Si
  • Results are valid for MOS, too ?
  • So, this presentation may interest you

3
Outline
  • Introduction self-heating
  • Measurement set-up
  • Self-heating modelling
  • Equivalent networks
  • Predictive model
  • Results, conclusion and perspectives

4
Introduction macroscopic
  • Self-heating
  • Heating of the device due to its power
    dissipation
  • Bipolar transistor
  • P IC VCE IB VBE
  • DT P ZTH

5
Introduction impact
  • Electrical Power -gt T changes
  • Temperature variation
  • Mobility variation
  • E-gap variation
  • IC, IB variation
  • Electrical power variation
  • Feedback convergence problems for electrical and
    physical simulators
  • Limit of operation in high power region

6
Measurement set-up step 1
-gt VCE(t)
  • Bipolar transistor

-gt VBE(t)
7
Calibration Measure VBE(T), step 2
  • IB const
  • VCE VCElow
  • Variation of T
  • 27C -gt 50C
  • Measure of VBE

8
Dynamic behaviour Trise(time)
  • From VBE(t)
  • And VBE(T)
  • -gt Trise (t)
  • New method which permits to take into account the
    temperature rise _at_ VCEVCEmin gt Mixdes05

9
Electrical modelling of Trise(t)
  • State of the art(VBIC, MEXTRAM, HICUM)
  • Results

10
New thermal self-heating model
  • The differential equation describing heat
    transfer is
  • ? thermal conductivity, W/mC
  • c specific heat, J/kgC
  • ? material density, kg/m3
  • T temperature, C
  • ?/c? thermal diffusivity, m2/s

11
Geometric presentation
Transistor, HBT
Schematic system representation with cylindrical
co-ordinates bidimensional axisymmetric geometry
Schematic system representation with Cartesian
co-ordinates
12
Boundary initial conditions
  • Initial condition t0,

13
Analytical problem resolution
  • Calculation of the thermal impedance
  • Trise(t) Pdiss(t) ZTH(t)
  • Transform into the Laplace domain and solution of
    differential equation

14
Comparison
  • Standard
  • Thermal impedance
  • Step response
  • New model
  • Thermal impedance
  • Step response

15
Results (1)
  • Comparison between the standard (double
    exponential) and new model
  • a 1E2B2C 0.5x10 µm device

16
Results (2)
  • Measurement for different Ib currents _at_ different
    power dissipation
  • a 1E1B1C 0.8x6.4 µm device

17
Equivalent networks
  • Electrical-thermal networks for SPICE
    simulation
  • Represent the thermal impedance as accurate as
    possible
  • Have as few parameters as possible
  • The parameters have a physical meaning

18
Equivalent network - recursive parallel
  • Recursive parallel network

19
Resultsrecursive parallel
  • Recursive parallel network
  • N10
  • RTH, R, C, k
  • 4 parameters have to be determined
  • Independent of cell number

-10dB/dec
- 45
20
Time domain
  • Step response of the parallel recursive circuit

21
Predictive Modelling
  • Calculate the thermal impedance as a function of
    the layout data
  • Numerical approach
  • Geometrical approach

22
Numerical approach
  • HBT cross section 3 layers
  • back end (Isolation and metallization)
  • Active layer (intrinsic transistor deep trench
    isolation)
  • Substrate
  • Resolving the Heat transfer equation with the
    specific initial and corner conditions

23
Results (RTH f(emitter area))
  • Physical approach
  • Numerical calculation takes some minutes
  • Actually some problems with CTH scaling

24
Geometrical approach
25
RTH calculation
26
Results output characteristics
27
HBT on SOI
Schematic Cross section
TEM Cross section view
28
Results - Layout investigation
Type Active surface µm2 E(emitter) Active E-surface µm2 RTH K/W
Q1 0.882 12 0.150.49 3100
Q2 0.8775 5 0.151.17 5400
Comparison to bulk Si HBT SOI 2 HBT bulk (!
Very rough estimation !)
29
Discussion
  • Limit of the standard model
  • Development of a new accurate model
  • Resolution of heat transfer differential equation
  • Physical model
  • Representation with equivalent networks
  • The parallel recursive network is very accurate
  • 4 parameters needed
  • Use in compact circuit modelling

30
Under work predictive model
  • Numerical approach
  • Geometrical approach
  • Both approaches give good results
  • Calculation time
  • Usability
  • Methods applied to HBT on SOI

31
Perspectives
  • Thermal coupling between transistors
  • Power device modelling
  • Layout optimisation
  • Investigation of the thermal behaviour of MOS
    transistors ? (cooperation)
  • Tools
  • Methods
  • Equations
  • Extraction methods

32
Thanks for your attention
  • The paper is open for discussion.
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