Liquid Crystal Measurement Instruments 2007 - Instec Inc

Liquid Crystal
Measurement
Instruments
2007
INSTEC ®
Focus on Excellence

Overview
The Liquid Crystal industry continues its explosive growth. The long awaited replacement of
CRTs has come and gone. Liquid crystal television dimensions grow to unprecedented sizes — both
at the large end and the small as hand held video players become ubiquitous. Liquid crystal displays
are everywhere from the laptop computer to the bathroom scale. At the same time LCs are
used in low volume high margin ‘niche’ applications for avionics, telecommunications, and tunable
lasers. The old standard TN mode display is not replaced but rather joined by IPS, VA, FLCs and
others. Competition is fierce and a competitor’s edge can depend on the quality and precise behavior
of the liquid crystal material, or rather mixture — for no pure LC is sufficient for any of these
applications — which it produces or employs. The accurate, simple and quick measurement of a
liquid crystal material’s physical parameters has become a necessity in today’s liquid crystal industry.
Based on more than thirty years of research experience from Prof. Noel Clark’s liquid-crystal
research group at the University of Colorado at Boulder, and twenty-two years of engineering and
design experience at Instec Incorporated, Instec has developed a line of liquid-crystal parameter
test instruments and accessories to meet your most critical requirements.
The ALCT3: A general purpose instrument for both industrial and academic research, capable
of automatically measuring the most important parameters of nematic (both positive and negative)
and ferroelectric liquid-crystals. For nematics, these include among others the bend and splay
elastic parameters K11 and K33, rotational viscosity (for positive dielectric materials only) and the
dielectric constants. For ferroelectrics, it quickly determines such parameters as the switching
time, polarization, and rotational viscosity.
The NNLCG1: A system specifically designed for measuring the difficult to determine rotational
viscosity of negative dielectric nematics.
The IV1: An instrument designed for LC material and display manufacturers. The IV1’s state of
the art electronics allows for the measurement of ion density, LC resistivity, voltage holding ratio
and residual DC.
The PD02: When added to the ALCT3, this photo detector allows for the measurement of
Transmission vs. Voltage (TV) curves and optical switching times.
Measurements over Temperature
Nematic liquid crystal parameters such as the elastic constants K11 and K33, the rotational viscosity
γ 1, along with ferroelectric liquid crystal parameters such as the polarization can be strong
functions of the temperature. The ALCT3, NNLCG1, and IV1 all make it simple to measure their
parameters over temperature. Each is easily integrated with the optional temperature controlled
shielding box (ALCT3-TS) or any of Instec’s signature thermal stages. The software allows the user
to go to a specific temperature for measurement or to setup a series of thermal measurements to
be carried out automatically. After a series of measurements the data can be viewed graphically
or saved to a text based file for later examination in any spreadsheet or data analysis package.
Liquid Crystal Cells and Cell Holders: A range of empty homogenous and homeotropic LC cells
with precise electrode spacing and area, ideal for the preparation of test samples. A range of homogenous
aligned in-plane switching empty cells are also available for the customer to choose.
Instec LC cell holders allow for the quick connection of our LC cells to any of the above instruments
without the need for soldering wires. Instec can also offer customized empty or filled LC
cells, and cell holders based on the customer’s specific requirements.
2

ALCT3 - USB Based Automatic Liquid Crystal Tester
Improved from the earlier PCI card versions of the ALCT1
and ALCT2, the new ALCT3 is an USB based instrument which
can be connected conveniently to both desktop and laptop
computers. The ALCT3’s easy to use software allows for the
measurement of both positive and negative-dielectic nematic
liquid-crystal materials, and the determination of material
parameters of ferroelectic LC materials as well. The range of
material parameters measured by the ALCT3 include:
For NLC (Positive Dielectric Anisotropic Material):
• Threshold voltage
• Splay and Bend elastic constants
• ε ⊥ and ε || dielectric constants
• Ion density and mobility*
• Rotational viscosity
• Electrical resistivity*
For Negative Dielectric Anisotropic Nematic Material:
• Threshold voltage
• ε ⊥ and ε || dielectric constants
• Electrical resistivity*
• Ion density and mobility*
• Splay and Bend elastic constants
For FLC:
• Electrical switching time
• Optical switching time
• Rotational viscosity
• Electrical resistivity*
• Dielectric constant
• Spontaneous polarization
• Ion density and mobility*
*Resistivity and ion density measurement of ALCT3 are designed for academic use only. The smallest current is only 1nA. For current
measurement down to 10pA, please refer to the IV1.
These parameters are of crucial importance to liquid crystal, and liquid crystal display manufacturers and researchers.
They help determine, among other things, the operating voltage of a display, the voltage spacing of visual ‘gray’
levels, and the speed or response time of a display.
The ALCT3 contains a versatile function generator and precision current sensor. Measurements are made by applying
specific waveforms to a liquid crystal cell, detecting the response current and employing the relevant equations of
liquid crystal physics. For example, after applying a series of AC voltages to a nematic liquid crystal cell to measure the
capacitance versus voltage curve, the curve is fit using the following integrals (H.J. Deuling, Mol. Cryst. Liq. Cryst. 19,
123, 1972) to determine the bend elastic constant K33.
2
C 2
2 Vth
φm
(1 + γ sin φ)(1
+ κ sin
= 1+
γ sin φm C π
V
∫0 2
2
0 sin φm
− sin φ
φ)
dφ
2
V 2
2 φm
1+
κ sin φ
= 1+
γ sin φm
dφ
Vth π
∫0 2 2
2
(1 + γ sin φ )(sin φm
− sin φ )
2
with
K ε||
κ = 33 − 1 Δ = ε − ε γ = −1
K
11
ε
||
⊥
ε ⊥
The ALCT3 can also be integrated with Instec’s microscope thermal stages and temperature controllers, enabling the
user to analyze the temperature dependence of the above parameters. The temperature controlled shielding box,
ALCT3-TS, is available as an optional accessory.
3

ALCT3 - USB Based Automatic Liquid Crystal Tester
Technical Specifications
Output Wave DC to 10KHz, voltage 0 to ±100V
Output Update Rate
500KHz
Output Resolution
16 bit
Input Resolution
16 bit
Input Sample Rate
500KHz
Current Measurement Range 1nA ~ 1mA
Current Sensing Resistance 10K, 100K, 1M, and 10MΩ
Current Resolution
100pA
Post Gain in the ALCT Box 1, 10, 100, 1000
Capacitance Measurement 2pF to 100nF
Easy-to-Use Software, WinLC
The ALCT3’s software has been designed to be both flexible enough for academic research and yet simple enough to
use for easy incorporation on the factory floor. For instance, in the Nematic Liquid Crystal measurement application the
data chosen to analyze for the determination of the dielectric constants ε || , ε ⊥, the elastic constants K11, K33, and the
threshold voltage can all be chosen by the user. Alternatively by the changing of a single setting they can be fixed to
default values to insure repeatable meaningful results.
Software Interface for CV Curve of Positive NLC
Software Interface for CV Curve of Negative NLC
4

ALCT3 - USB Based Automatic Liquid Crystal Tester
Software Interface for Gamma1 Measurement (Positive NLC)
Software Interface for Function Generator/Oscilloscope
Software Interface for FLC Polarization Measurement
Software Interface for FLC Switching Measurement
5

NNLCG1 – Rotational Viscosity for Negative NLC
With the advent of projection and direct-view large-sized
liquid-crystal monitors and televisions the vertically aligned
mode has come into prominence and with it the negative dielectric
liquid crystals on which it relies. One of the most critical
parameters for any LC is γ , the rotational viscosity, which
greatly influences the time response of the display. However,
measuring the rotational viscosity of negative dielectrics has
traditionally been difficult due to such switching phenomena
as backflow and the like. Instec designed the Negative
Nematic Liquid Crystal γ 1 test instrument specifically to overcome
this problem. With it, one can quickly and accurately
measure the rotational viscosity of negative dielectric materials
in seconds.
The rotational viscosity is a parameter particularly sensitive to temperature. As with all Instec liquid crystal measuring
instruments, the NNLCG1 integrates easily with either the ALCT3-TS temperature controlled shielding box or our
standard temperature controlled stages.
Technical Specifications
Output Wave 1 KHz, voltage 0 to ±100V
Output Update Rate
500KHz
Output Resolution
16 bit
Input Resolution
16 bit
Input Sample Rate
500KHz
Current Measurement Range 1nA ~ 1mA
Current Sensing Resistance 10KΩ
Current Resolution
100pA
Post Gain in the ALCT Box 1, 10, 100, 1000
Capacitance Measurement 2pF to 100nF
Easy-to-Use Software
6

IV1 - LC Tester for Ion, Resistivity, VHR, and RDC
Instec designed the IV1 specifically with the industrial customers in
mind. Its electronics are capable of exceedingly sensitive current
measurement and low leakage voltage measurement. Its cables and
connectors are triaxial in order to allow guarding against external leakages.
The IV1 can be configured to measure any or all of the following:
• Ion Density
• Liquid Crystal Resistivity
• Voltage Holding Ratio (VHR)
• Residual DC (RDC)
Ion density and liquid crystal resistivity are critical components in the proper functioning of any LC display but especially
active matrix LCDs. With too many contaminant ions or too low a resistivity, displays are prone to problems such
as image retention and flicker. These measurements are useful to LC manufactures both in the development of liquid
crystals and quality control. In addition, display manufacturers can use them for both incoming and in line quality inspection
and as a diagnostic tool to trace down root causes of problems on the line.
VHR and RDC are a more direct probe for potential problems. Lowered Voltage Holding Ratios can result in noticeable
flicker to a display user. Elevated Residual DC values can also produce flicker and/or image retention (or image
sticking).
In measuring VHR, the IV1’s built in function generator outputs to the sample under test an AC pulse train of user
adjustable frequency, amplitude, and duration. Simultaneously, the IV1’s internal electrometer senses changes in voltage
on the sample, in particular the voltage droop between pulses. For the measurement of RDC, the IV1 applies a set
DC voltage to the liquid crystal cell of user selectable magnitude and duration. The built in electrometer then records
the residual DC voltage left on the sample cell, again for a user selectable duration. Since the duration of the initial DC
voltage may be an hour or more, while the measurement time may be set to ten or more minutes, a single RDC determination
can be a long process. With that in mind we designed the IV1’s electronics with a modular structure and options
exist to add up to 8 channels.
Technical Specifications
Ion/Resistivity
Voltage (Min)
Voltage (Max)
Resolution
Frequency
Current Range
Current Resolution
Electrical Connections
Voltage (Min)
Voltage (Max)
Resolution
Output Current
Offset Voltage
Input Capacitance (Hold Mode)
Leak Current (Hold Mode)
V.G Offset (Hold Mode)
Charge Injection
Electrical Connections
± 10mV
± 10V (± 100V optional)
100 μ V
0.01 ~ 1kHz
100pA to 1mA
1pA
Triaxial
Voltage Holding Ratio / Residual DC Voltage Measurement
± 10mV
± 10V
100 μ V
± 100mA (Max)
± 0.1mV
< 1pF
< ± 0.1pA
± 0.1mV
± 5pC
Triaxial
7

PD02 C-Mount Photo Detector
The addition of the PD02 photo detector expands ALCT3’s capabilities to include the optical measurement of transmission
versus voltage curves and switching times. This low noise high speed photo detector comes C-mount ready for
attachment to a microscope and also includes a standard 1/4-20 tapped hole for easy mounting to an optical table.
Fully integrated into the ALCT3’s software, switching between electrical and optical measurements can be done with
a click of the mouse.
Features
• 1 μs Response Time
• Easy To Use
• Differential Output
• 4 Post-gains To Choose
• Microscope C-mount Ready
• ¼-20 Tapped Hole For Horizontal Mounting
Technical Specification
Response Speed
Post Gain
Input Voltage
Output Voltage
Mounting
1 μs with post gain X1
x1, Rf = 10 KΩ; x10, Rf = 100 KΩ; x100, Rf = 1 MΩ; x1000, Rf = 10 MΩ
100V ~ 240 VAC
10V
C-mount for microscope or ¼-20 for horizontal mounting
X1000
X100
X10
X1
8

Liquid Crystal Cells and Cell Holder
Instec provides a lineup of empty liquid crystal test cells ideally suited for use with
the ALCT in addition to other LC research applications. When measuring a liquid crystal’s
parameters, sample preparation is as critical to the measurement as the testing
instrument itself. Instec’s cells are manufactured with patterned electrodes in industry
standard clean rooms and equipment. This yields a cell whose active sample area is
known precisely, has low parasitic capacitance, and can be completely filled with the LC
material under test.
Even so, the reliance on spacers to determine cell gap can lead to errors of several
percent. Thus for critical testing applications, Instec makes available calibrated cells
whose spacing have been individually measured both optically and electronically. Each
calibrated cell is then shipped along with its individual cell thickness and parasitic capacitance.
The adhesive of Instec cells can withstand up to 200ºC. Alignment layers are of 1º to
3º pre-tilt angles. Physical dimensions and spacing of cells vary depending on different
models. Cell gap tolerance is ±0.2 µm.
Image above is an example of
LC1, 90° twist aligned.
PI Type
Homogenous Alignment
90º Twist
Homogenous Alignment
Parallel
Homogenous Alignment
Anti-Parallel
Homogenous Alignment
Anti-Parallel
Homeotropic Alignment
Anti-Parallel
Part No
ITO Area
(mm)
Cell Spacing
(microns)
LC1-6.0
6.0 µm
5 X 5
LC1-6.8 6.8 µm
LC3-5.0
5 µm
LC2-5.0 5 µm
LC4-6.8
5 X 5
6.8 µm
LC2-9.0 9 µm
LC2-20.0 20 µm
SA025A04uG180 5 X 5 4 µm
SA100A09uG180 10 X 10 9 µm
SA100A18uG180 10 X 10 18 µm
SA025A04uT180 5 X 5 4 µm
SA100A09uT180 10 X 10 9 µm
SA100A18uT180 10 X 10 18 µm
No PI (Patterned ITO) SA100A04uNOPI 10 X 10 4 µm
In-Plane-Switching
Homogenous Alignment
Vertical Rubbing to Electric
Field
In-Plane-Switching
Homogenous Alignment
Parallel Rubbing to Electric
Field
IPS02A09uGVE 10 X 10 9 µm
IPS02A18uGVE 10 X 10 18 µm
IPS02A09uGPE 10 X 10 9 µm
IPS02A18uGPE 10 X 10 18 µm
ITO
Resistance
Cell Outer Dimensions
(mm) &
Cell Holder Model
100 Ω/□ 15.25 X 20.25 X 2.25
100 Ω/□ 15.25 X 17 X 1.5
30 Ω/□
21 X 25 X 1.5
Cell Holder: LCH2
Image above shows the structures
of LC2, LC3, and LC4 empty cells.
Image above shows the structures
of SA Series empty cells. Example
is SA100
LCH2
Instec LC cell holder, LCH2 accommodate various Instec empty cell models: SA025,
SA100, and IPS02. The cell holder can be used inside the Instec microscope hot and
cold stages. The LCH2 has external electrical grounding for electrical noise shielding.
The LCH2 can be used to attach electrodes to the LC Cells. Otherwise, solder or silver
epoxy can be used to attach wires.
How to Use Instec LC Cells
There are two openings on Instec liquid crystal cells. Heat the cell above the isotropic temperature of your LC material.
Then drop a very small amount of LC material on one opening of the Instec empty cell. The capillary force will suck LC
material into the empty cell. It may take a few minutes before the cell is fully filled. You can see the filling process at
"right" angle under light. Once the cell is filled, in order to get good alignment, please cool down slowly, especially during
the phase transition temperature.
9

TS62 Microscope Thermal Stage
All of Instec’s Liquid Crystal Measurement Instruments work not only with the ALCT3-TS temperature controlled
shielding box, but also with Instec’s full line of Thermal microscope stages, plates and chucks. A popular choice for liquid
crystal research and development is the TS62. This microscope thermal stage’s built-in peltier heating/cooling unit
adjusts temperature from -30 o C to 120 o C, a range sufficient for nearly all commercial LC research and development.
The TS62 boasts a large sample area, adjustable sample chamber height, and fast heating and cooling rates. With the
TS62 not only can an LC sample’s parameters be measured over its entire operating temperature range but it can be
studied under the microscope as well. (Note: if a wider temperature range is required Instec has units with ranges available
from -190 o C to 700 o C).
Features
• Peltier-Based Microscope Thermal Stage
• Programmable Precision Temperature Control
from -30ºC to 120ºC with 0.1ºC Temperature Precision
• Accommodates Up to 1.5"X2.0" Sample Size
• Fast Heating and Cooling Rate
• Variable Sample Chamber Height
• Large Viewing Window
• Configured with STC200 Standalone Temperature
Controller with RS232 Communication Port and Windows Based Software
• Optional IEEE488 Communication Port
• Free LabVIEW Drivers for IEEE488 and RS232
Technical Specifications
Temperature Control Sensor
Platinum RTD
Control Method
PID, variable DC power output
Temperature Range -30°C to 120°C
Temperature Precision
0.1°C
Temperature Stability ±0.1°C at 37°C
Minimum Heating and Cooling Rate ±0.1°C/Hour
Maximum Heating Rate +50°C/Min. at 37°C
Maximum Cooling Rate -50°C/Min. at 37°C
Minimum Working Distance
2.5 mm when using double glass windows on the cover
1.6 mm when using single glass window on the cover
Minimum Condenser Distance 17 mm
Sample Chamber Height
2.5mm, increasable to 11.5mm
Sample Area 1.5" X 2"
Sample View Aperture
0.2" (5 mm) for transmitted light
0.8" (20mm) for reflected light
10

TS62 Microscope Thermal Stage
Cross Section View
Stage height H: 1.1"
Working distance F:
2.5 mm
Working distance for condenser C: 17 mm
Mounting Hole Pattern
11

ALCT3
For NLC (Positive Dielectric Anisotropic Material):
• Threshold Voltage
• Splay and Bend Elastic Constants
• ε ⊥ and ε || Dielectric Constants
• Ion Density and Mobility
• Rotational Viscosity
• Electrical Resistivity
For Negative Dielectric Anisotropic Nematic Material:
• Threshold Voltage
• ε ⊥ and ε || Dielectric Constants
• Electrical Resistivity
• Ion Density and Mobility
• Splay and Bend Elastic Constants
For FLC:
• Electrical Switching Time
• Optical Switching Time
• Rotational Viscosity
• Electrical Resistivity
• Dielectric Constant
• Spontaneous Polarization
• Ion Density and Mobility
NNLCG1
• Rotational Viscosity (Gamma1) for Negative
NLC material
IV1
• Ion Density
• Resistivity
• Voltage Holding Ratio
• Residual DC
PD02
• Transmission vs. Voltage (TV) Curve and
Optical Switching Time
Liquid Crystal Cells & Cell Holder
TS62 Microscope Thermal Stage
Instec, Inc.
5589 Arapahoe Avenue #208
Boulder, CO 80303
USA
Represented By:
Phone: +1 303-444-4608
Fax: +1 303-444-4607
E-mail: sales@instec.com
www.instec.com