Gooch displays

Gooch and Tarry plot of transmission versus the coefficient, u, and the corresponding birefringence values, An, for a Twisted Nematic Liquid Crystal Display TN-LCD of thickness 6.55 pm operating between parallel polari-... 

For the lowest order m = 1, dAnJX = Vlll. This is the Gooch-Tarry s first minimum condition for the 90° TN cell. For the second order m = 2 and dAn = v/l5/2. The second minimum condition is used only for low-end displays such as wrist watches, because a large cell gap is easier to fabricate, and the cyano-biphenyl LCs are less expensive. For notebook TFT-LCDs, the first minimum is preferred because fast response time is required. 

Differential Scanning Calorimeter n (DSC) An instrument that measures the rate of heat evolution of absorption of a specimen while it is undergoing a programmed temperature rise (Gooch, 1997). A recorder displays the data as a trace of increase in heat per increase in temperature (d /dT) versus temperature. An example of a DSC thermogram of polypropylene is shown. The DSC has been used to study curing reactions and related properties of thermosetting resins, and heats of decomposition of resins. (An example of a DSC instrument is the PerkinElmer Diamond DSC. 

In a twisted nematic display, the cell is constructed with a dAn product close to a point on the Gooch-Tarry curve that provides ideal rotation of light at visible wavelengths, i.e. with a dAn value usually close to 0.55 pm or 1.05 pm. Placed between two crossed polarizing films with their axes aligned with (or perpendicular to) the alignment directions at the cell surfaces, the resulting rotation of the optical plane of pola-... 

Figure 2. Gooch and Tarry curve for a normally black mode operated TN display.

For the NB mode, intensity minima of the transmitted luminance are calculated for dAn=0.48 pm, 1,09 pm and 1.68 pm which correspond to the minima of the Gooch and Tarry transmitted intensity for a wavelength A=0.55 pm. Operation in the 1 st minimum is mostly used in TFT displays as it offers a wider viewing angle [15, 16]. The 2nd minimum condition is used in watches and calculators. 

With regard to the dye-related parameter measurements, the dye concentration is usually kept at about 0.5-2%, depending on its absorption coefficient. For azo dyes the dye concentration is about 0.25-1% for dye doped TN, about 2-4% for Heilmeier displays, and about 2-5% for phase change displays. The cell thickness is usually about 5 pm for dye-doped TN at the first Gooch Tarry minimum [ 15,16,88], about 7-10 pm for dye-doped TN at the second Gooch Tarry minimum [15, 16, 88], about 5-15 pm for Heilmeier, and about 10-20 pm for phase change dichroic displays. Usually, the dye concentration is increased by a factor of about 1.5-2 when anthraquinone dyes are used instead of azo dyes, as anthraquinone dyes have less absorbance than azo dyes. Sometimes combinations of azo and anthraquinone dyes are used [16, 54]. 

The threshold characteristic of the dye-doped TN display is very similar to that of a TN display (see Fig. 4). The contrast ratio of a dye-doped TN LCD is heavily dependent on the polarization efficiency of the polarizer, and thus polarizers with very high polarization efficiency (>99%) should be used. The threshold and operating voltages also increase slightly with an increase in thickness. The contrast ratio shows a similar effect to the Gooch Tarry curve in TN displays. The contrast ratio has been found to maximize at the first and second Gooch Tarry minima [16, 88]. It has been found that the incorporation of dyes broadens the Gooch Tarry minima [16, 27]. The addition of a small amount of dichroic dye decreases the values of the maxima and increases... 

C. H. Gooch et al., A Storage Cathode-Ray Tube with Liquid Crystal Display, J. Phys., D6, p. 

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