Liquid Crystal Measurement Instruments 2007 - Instec Inc

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.
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