The Effect of Polyimide Fixation on Thermal Performance of GaAs Cantilever Based MEMS: A 3D Numerical Analysis with DEETEN

1
Title

• The Effect of Polyimide Fixation on Thermal
  Performance of GaAs Cantilever Based MEMS A 3D
  Numerical Analysis with DEETEN
• Eduard Burian1 and Tibor Lalinský2
• 1 LOX Technologies, Bratislava, Slovakia,
  www.loxtec.com, mail_at_loxtec.com
• 2 Institute of Electrical Engineering of SAS,
  Bratislava, Slovakia, eleklali_at_savba.sk

2
Contents

• Introduction
• Basics of DEETEN
• Studied MTC MEMS
• Results of DEETEN Simulations
• Conclusions

3
Introduction

• In the first part of this presentation, we refer
  of a novel simulation technology DEETEN, of its
  principles and implementation for thermal
  analysis of micromechanical systems.
• In the second part, we refer of results of
  DEETEN 3D thermal analysis of a GaAs
  Micromechanical Thermal Converter, particularly,
  to analysis of thermal effect of polyimide
  fixation of the cantilever beam of this MEMS.

4
Basics of DEETEN

• Differential Equations Efficient Treatment by
  Eliminative Nesting
• is a novel software simulation technology
  capable of efficient multi-million-point 3D
  simulations on a conventional PC. It takes simple
  math of finite difference method and field
  relaxation algorithms together with modern
  software technologies to achieve impressive
  computational performance.
• The efficiency and performance of DEETEN is
  achieved by
• recursive domain decomposition of simulation
  space
• topology and field complexity is considered in
  created domain chain
• multigrid capability, pre-computed field is
  smoothed on finer meshes
• simple discretization algorithms based on finite
  differences method
• solution to PDEs by field relaxation algorithms
• computer-friendly (octree) domain structure
  defined by means of OOP

5
Basics of DEETEN / the D10 domain

• D10 domain consist of 10x10x101000 mesh points
• from those 8x8x8512 points are inner
• 6x8x8384 of the outer points contribute to
  solution of PDEs
• in a parent domain, up to 8 smaller child domains
  can exist
• the child domain is half the size of the parent
  domain
• inner volume of a child matches perfectly with
  one inner parent octant
• domain chaining can go on till desired spatial
  resolution is achieved

6
Basics of DEETEN / domain overlapping

• Defined conditions assure that two neighboring
  child domains are overlapped so that a part of
  the boundary of one child domain covers with the
  first plane of inner points of the other, even in
  the case they have no common parent. Inner
  volumes of child domains, which never overlap,
  create a smooth simulation mesh necessary for
  sequential (domain-by-domain) treatment of PDEs.

7
Basics of DEETEN / 3D domain structure

• example of domain structure by cantilever MTC
  simulation
• upper level domains only

8
Studied MTC MEMS / topologies

• Micromechanical Thermal Converter (MTC) is being
  developed as key par of the Microwave Transmitted
  Power Sensor (MTPS) at Institute of Electrical
  Engineering of SAS. We studied two MTC
  topologies
• 1. cantilever-based MTC
• two 1-2?m thin GaAs cantilevers with
• HFET heaters
• polyimide-enhanced mechanical stability
• 2. isolated membrane-like MTC
• GaAs island 1?m thin is floating
• on polyimide membrane

Contact pad
pHEMTTemperature sensor
pHEMT - Heater
Polyimide membrane
Cantilever
Polyimide membrane
9
Studied MTC MEMS / simulation conditions

• MEMS were kept in air and ambient temperature is
  300K
• air thermal conductance is included into model
• power dissipation in a HFET heater is set to 1mW
• Cantilever MTC
• main domain dimensions 1.6x1.6x0.16mm
• domain level limit set to 5, i.e. spatial
  resolution 1256 at maximum
• typically 1500 domains were created, with 1.5M
  mesh points
• in comparison, regular rectangular mesh requires
  256316.7M points
• Membrane-like MTC
• main domain dimensions 1.0x1.0x0.1mm
• domain level limit set to 6, I.e. spatial
  resolution 1512 at maximum
• typically 2500 domains, 2.5M mesh points
• in comparison to regular rectangular mesh with
  5123134M points

10
Results of DEETEN simulations / cantilever MTC

• Polyimide-fixed cantilever beams TMAX9.96K
• Non-fixed cantilever beams TMAX10.11K
• Polyimide-induced degradation does not exceed 2
  
• Heat dissipation through metallic leads results
  is 40

11
Results of DEETEN simulations / membrane-like MTC

• Maximuim temperature in center TMAX16.76K
• Effective thermal resistance 13K/mW

12
Conclusions

• In thermal investigations of two design of a MTC
  MEMS, DEETEN has been proven as viable and
  promising technology.
• Joining advanced numerical methods for PDE
  solving with modern, object-oriented software
  technologies can substantially improve
  computational performance in electrophysical
  simulations.
• Next plans
• more detailed thermal investigation of MEMS
• details in 100-10nm range
• simulation of complex thermal, electronic and
  mechanic phenomena
• integrated simulation visualization environment