clex22.in : Liquid Crystal (LCD) Field Dependent Capacitance
Requires: CLEVER, VICTORYPROCESS
This example illustrates using Clever to simulate the physics in Liquid Crystal films. Liquid crystal films consist of long molecules, called directors which rotate in response to applied electric fields, that effectively supplies a rotational torque. The permittivity and hence the capacitance of these LCD films, is highly directional and dependent on the the orientation of the long molecules (directors). When an electric field is applied which rotates these molecules, the capacitance in the direction across the film, can change dramatically. Clever simulates this physics, in order to calculate the voltage (field) dependent capacitance of LCD layers.
The directional permittivities of the LCD versus director angle are defined in the setLC statement.
The layers which interface the LCD film can anchor the LCD molecules in a fixed direction, regardless of applied field. This creates an increasing angular rotation of the LCD molecules with applied field, the further they are away from these anchored interface regions. These physical effects are also included in the simulations. Specifying these fixed interface angles for top and bottom interfaces is executed by the statements LCbndaryT and LCbndaryB
Clearly, if an applied voltage changes the permittivity of a film, the stored charge and capacitance is also voltage dependent. Since Q=CxV, where Q is stored charge, C is layer capacitance in a particular direction and V is applied voltage, mathematical instability can result at certain applied voltages due to the inter-dependence of all three parameters. The purpose of the cPenalty parameter, is to introduce a modicum of numerical damping, to calm these numerical instabilities.
To load and run this example, select the Load button in DeckBuild > Examples. This will copy the input file and any support files to your current working directory. Select the Run button in DeckBuild to execute the example.
Input Deck
# This example demonstrates the LC director calculation
# of a super in-plane switching (S-IPS) cell.
# The pixel electrodes of the S-IPS cell
# consist of two zigzag ITO electrodes.
go VictoryProcess
Init material="oxide" GasHeight=5 Depth=1 from="0,0" to="10,10"
SpecifyMaskPoly maskname=Pixel p1="3,5" p2="4.5,10" p3="2.5,10" p4="1,5" \
p5="2.5,0" p6="4.5,0" electrode="Pix"
SpecifyMaskPoly maskname=Common p1="8,5" p2="9.5,10" p3="7.5,10" p4="6,5" \
p5="7.5,0" p6="9.5,0" electrode="Com"
line x location=0 spac=0.25
line x location=10 spac=0.25
line y location=0 spac=0.25
line y location=5 spac=0.2
line y location=10 spac=0.25
line z location=-5 spacing=1
line z location=-4 spacing=1
line z location=-3 spacing=0.025
line z location=-2.95 spacing=0.025
line z location=-1.5 spacing=0.1
line z location=0 spacing=0.1
line z location=1 spacing=1
deposit material="LC" thick=2.95 min
# Pattern the pixel electrodes.
deposit material=ITO thick=0.05 min
etch material=ITO thick=0.05 min Mask=Pixel
electrode mask=Pixel material="ITO"
deposit material=oxide thick=0.05 max
etch material=oxide thick=0.1 max Mask=Common reverse
deposit material=ITO thick=0.05 min
electrodes mask=Common material=ITO
strip oxide
deposit material=LC thick=0.05 min
deposit material=oxide thick=1 min
save name=clex22_0
## Create a Conformal Mesh Structure File ##
go victorymesh
load in=clex22_0
remesh conformal
save out=clex22_1.str
## Now Analyze LC Characteristics ##
go clever
set penalty=1000
Init structure="clex22_1.str"
material ITO conductivity=1000
material oxide permittivity=3.9
# Specify the anisotropic permittivity and the elastic constants of the LC.
setLC epsParaDir=10.7 epsVertDir=3.7 splay=14.4e-12 twist=6.9e-12 \
bend=18.3e-12 cPenalty=$penalty
# Specify the rubbing angle and the pre-tilt angle
# on the top and at the bottom of the LC region.
LCbndaryB partition(0 10) rubAngle(90) tiltangle(1)
LCbndaryT partition(0 10) rubAngle(90) tiltangle(1)
solver linearsolver=pam pamsolver=gmres ddprecond=RAS preconditioner=amp \
multilevel=0 fillratio=1.e-3 lsmaxiter=200 lstolerance=1.0e-10 \
nlsmaxiter=100 nlstolerance=1.0e-8 topDirichletBC
option LSconvergeinfo=1 NLSconvergeinfo
# Ramp the pixel voltage to 6V with a step of 0.5V until 2V
# and of 0.25V thereafter.
setPixelBias("Pix",0,0.5,1,1.5,2,2.25,2.5,2.75,3,3.25,3.5,3.75,4,4.25,4.5,4.75,5,5.25,5.5,5.75,6)
# Save the structure at each 1-volt interval from 0 to 5V.
Interconnect Capacitance domainboundarycondition=cyclic savestep=1 structure="clex22"
# Save the parasitic capacitance netlist.
save spice="clex22.net"
tonyplot3d clex22.V6.str
tonyplot clex22.net