NONEMISSIVE DISPLAY MATERIALS IN THE FSU

Materials expertise in the FSU is a long-established fact. Indeed, the panelists saw evidence of this for strategic solid- state materials at ELMA in Zelenograd. (See site report on ELMA, Appendix C.) ELMA considers (and will show) that its solid-state materials expertise is better than that of the United States and only slightly behind that of Japan.

It was interesting to learn that the largest supplier of silicon substrates in the world is German. Germany has always led the world in the production of chemicals (Chandler 1990). Indeed, Merck is now the largest supplier of liquid crystal materials (Footnote 14).

About thirty different liquid crystal states of matter are known at this time. Of these, the three states used in displays are nematic; its equivalent chiral state, cholesteric (N*, actually the state used in STN); and smectic C*. (See Liquid Crystal and Other Nonemissive Displays.)

Observations about FSU flat panel display technology are summarized in Table 2.1. In this table, P indicates ongoing mass production for products with customers as distinct from small-scale or prototyping production for potential customers, indicated by (P), with the products also in brackets. A selection of the R&D efforts in various aspects of materials used in liquid crystal displays that the panel was exposed to are described in the following sections.

Table 2.1
Liquid Crystal Display Material

Low Molecular Weight Liquid Crystals

Each one of the FSU countries that panelists visited had its internal source of LC materials for displays. Niopik and Riap are suppliers in Russia and Ukraine. (See site report on Niopik.) The Sevtchenko Institute supplies Belarus' LCD enterprise.

Niopik and Switzerland's Hoffmann-LaRoche (itself a liquid crystal supplier) have a collaboration with Martin Schadt, a contributor to the world patent for TN displays (expired 1991) who is world famous for his structure-property expertise, the relationship between macroscopic properties of liquid crystals and molecular structure (Schadt 1993). All three chemical sources had either access to or their own facilities to characterize LC materials for display applications.

Production. Large quantities of various liquid crystal materials are manufactured by Niopik in Russia. A large variety of liquid crystals are made at the Sevtchenko Institute in Belarus. Cyanobiphenyls are made at Riap, fluorinated liquid crystal materials at the Physical Chemistry Institute, and chiral compounds at the Institute of Monocrystals, all in Ukraine.

It is not clear that chemicals supplied by academic institutes have the volume needed for production, hence the bracket around the P in the column for Belarus.

Basic Research. Basic research at the Moscow Institute of Fine Chemical Technology elucidates fundamental mechanisms responsible for the temperature range of the nematic state. While WTEC panelists knew of similar, more broad-based work from the former Sackmann and Demus group (Halle) in the former East Germany, it was interesting to learn that more than ninety Ph.D. theses have emerged from this institute on topics focused on liquid crystal display relevance. (See site visit report on Moscow Institute of Fine Chemical Technology, Appendix C.)

More broadly-based research was also discussed in Ukraine.

Device Research at Niopik. There was an interesting demonstration of a memory effect in a smectic C* sample that was thick compared to its pitch when the substrates were treated with a photopolymer (see below), then irradiated with polarized light to determine liquid crystal alignment (Voruflusev et al. 1993). Its response time was about 10 microseconds. Platan is developing a 64 x 48 mm light shutter using this effect.

Smectic C* is popularly but incorrectly known as "ferroelectric." Canon (Japan) has been developing this technology for the last eight years, and has succeeded in making large (21" and 27"), nearly video-rate liquid crystal displays with color. Power consumption (about 50 W) is not an issue for these large area displays not destined for portable applications, as are the antiferroelectric displays.

Colorful ferroelectric displays are not so easy to make as TN displays. Their main advantage seems to be that they do not use MIMs or TFTs to switch; they are passive displays. They also require a different drive scheme and more than three pixels to make a color display that does not flicker or look unfocused. There are many paintings from the Impressionist School, particularly from Seurat, shown on these displays.

Canon virtually had to reinvent nearly all aspects of LCDs to make its products, which include a well-engineered suspension for the display panel. Unlike TN displays, once the surface- determined alignment is disturbed, by mechanical shocks for example, the smectic C* material becomes disordered and loses its electro-optic effect. Anyone who has touched their TN or STN screens knows that this only causes a small transient in these displays that quickly return to their undisturbed state. If the photopolymer treatment addresses this issue, this is an important step forward for this display technology (Footnote 15).

Polymeric Liquid Crystal

Polymeric liquid crystal is novel material for which the technology now exists to obtain optical grade monodomain liquid crystal polymer films to make, for example, compensators for STN displays (retardation films) (Toyooka et al. 1993).

Shibaev's group at Moscow State University has suggested that its slow electro-optic response also makes these materials useful as storage devices and electron resists (Yusupov et al. 1993). Another resource on the works of Shibaev's group is in a large book dedicated to liquid crystal polymers translated from Russian by S.L. Schnur (Shibaev and Byelyavev 1990).

For another comparison with work on these and similar materials outside the FSU, see the work of Finkelmann's group in Freiburg, Germany. This work has developed in a somewhat different direction. For example, the scientists demonstrated piezoelectro-optic effects in cholesteric liquid crystal elastomers: Unstressed, the material is translucent; when stretched, it becomes transparent (Meier and Finkelmann 1991). H.R. Brand (Bayreuth, Germany) had predicted that this effect should exist in cholesteric liquid crystal elastomers because they cannot use flow to dissipate mechanical stress (Brand 1989).

The panel did not see work on PSCT, but the polymer dispersed liquid crystal (PDLC) (Doane 1992; ALCOM 1991, 1992), a one-pixel privacy screen, was amusingly presented by Belyaev at Niopik. As this film was dried down (see Niopik site report), the technology to make this pixel sounds more similar to the NCAP technology of RayChem. This pixel was in a picture frame. In the off-state, a smooth white tile was in the frame; in the on-state, one of the standard colorful pictures (on paper), with bottles and colorful fruit used to demonstrate electronic display capability, popped into the frame. The panelists were delighted. The presentation underscored novel interior design possibilities for these materials.

Alignment layers refer to a thin layer of organic material between the liquid crystal and the display electrodes on the glass substrate. The orientation of the liquid crystal optic axis at the substrate is determined by mechanically buffing the alignment layer. (See Liquid Crystal and Other Nonemissive Displays.)

The panelists' understanding is that buffing sets up an easy direction for the liquid crystal optic axis by creating a parallel array of grooves or channels to guide the nematic's optic axis (Berreman 1972). Recently it was announced that parallel grooves using photoresists could be made, resulting in LC orientation that was as good as with the buffing technique (Toshiba Announcement 1992). Uchida et al. at Tohoku University discuss a stamping method to create grooves that also control pretilt (Lee et al. 1993).

"Pretilt" refers to the LC optic axis being slightly (approx. 3-5 degrees) out of the electrode plane. Its effect is to essentially remove the threshold in the Freedericksz transition, thus reducing hysteresis and the slope of the electro-optical response (more colors) at lower drive voltages, and to prevent domain wall formation (Rapini and Papoular 1969).

The novel idea to orient the LC optic axis at glass substrates involves first coating them with a photopolymer that is then irradiated with polarized light (Schadt et al. 1992). The polarized light exerts sufficient torques to arrange specific chemical groups of the polymer on the glass. When a liquid crystal is sandwiched between glass slides that have been treated in this manner, its optic axis is perpendicular to the direction of the polarization used to arrange the chemical groups.

Reznick (Ukraine) has proposed a way to control the pretilt of the director at the substrate (up to 15 degrees), making this technique a novel and clean way to mass-produce oriented LC samples without buffing, leaving open only the question of cost. (See Liquid Crystal and Other Nonemissive Displays.)

The P in Table 2.1 for alignment layers is in brackets because production is contingent on how the market develops.

Another strategy is to avoid alignment layers altogether (Toko et al. 1993).

Color Filters

Another interesting idea for photopolymerizable materials has been proposed in a collaboration with Saratov State University, Niopik and Hoffman-LaRoche, as in situ color filters in STN LCDs (Yakovlevl et al.). The panel did not see color STNs made in the FSU, but FSU scientists are thinking about it and developing novel strategies for bringing color to STN.

It was also interesting to learn that researchers in Belarus thought organic materials that include a metal atom, organometallics, could be useful for color filter technology. Organometallics are used in cancer chemotherapy, which means that they probably need to have their carcinogenic potential evaluated. (The blood's hemoglobin is probably the most familiar organometallic known). They are nontrivial materials to synthesize. The relevant information needed here to evaluate feasibility in manufacturing are safety, materials' lifetime, and cost.

Since color displays are not in production in the FSU, the P is in brackets for this materials technology. The technology exists, but has not yet been transferred to production.

For an overview of color filters used in the display technology in Japan, see Doane's chapter in the JTEC evaluation (Tannas and Glenn 1992).

Retardation Layers

Retardation layers or quarter wave sheets were first proposed for STN in 1986 (Footnote 16), and in 1989 for TFT LCDs (Yamaguchi et al. 1989). Retardation layers are a requisite for STN displays, which look rather blue without them. So, since this is a well-known way to correct this problem, the panel has determined that there is production capacity at Niopik, which produces uniaxial and biaxial filters that act the same way. Niopik also has a computer program similar to the one set up by Larimer et al. (1994) to simulate display quality from the user's perspective (Berreman 1972; Berreman and Scheffer 1970). The groundwork is being carefully laid in Russia to tackle more demanding display technologies.

TN indicators and small alphanumeric displays do not require retardation layers for viewability. So, while the Ukraine also has the capability to make these filters, it was not clear that there was a customer base for them, since they do not make STN displays, hence the (P).

Polarizers

Polarizers from Nitto Denko (Japan) are now used in the LCD production at Saratov. Niopik representatives said that they could also supply polarizers (see Niopik site report) in large volume. Polarizers used in the Ukraine industry are also internally supplied.

Novel colorful polarizers are available at the Institute for Physical Problems, Zelenograd, and are made using a Langmuir- Blodgett technique, which could have novel applications in LCDs. (See site report for Institute for Physical Problems, Zelenograd.)

Spacers

Etching glass down to make spacers needs to be evaluated for mass production.

Sealants

This is an important item for packaging LC displays. Panel members did not hear any information on how LCDs are sealed in the FSU.

Substrates

Glass substrates. Ordinary glass from internal sources appears to be widely used. At Saratov, scientists treat the glass further to obtain the thickness and uniformity needed for their STN display line (see site report for Zelenograd Institute of Physical Problems, Appendix C). While ordinary glass may be more than adequate for mass production of low resolution displays, or even MIM production, which has considerably fewer processing steps, transfer to mass production of active matrix displays needs to be evaluated. In view of research in Japan on the quality of glass for TFT LCDs, it seems unlikely that ordinary or soda-lime glass could survive the demands of many lithographic steps with its many chemical washes, and the large temperature ranges of the many processing steps required in a TFT processing. If it could, one suspects that such a process would have been implemented already in Japan.

Other aspects of glass substrates for optimization of display viewability are that it be transparent to a wide range of optical wavelengths and nonreflecting. Polymer substrates. The WTEC panel did not learn anything more about polymer substrates in the FSU. To meet the growing need for portable displays, the move to plastic substrates for STNs is one of the trends for improving this technology. Sharp announced its plans to release a 4.9-inch STN plastic LCD in the spring of 1994 that is "half as heavy and two thirds thinner" than a comparable glass model (Journal of Electronic Engineering 1993). LCDs with 336 x 240 and 640 x 480 (VGA) pixels will be available.

Quartz substrates. Quartz substrates are mainly used to make polysilicon TFTs since the temperatures to process them are much higher than they are for amorphous silicon TFTs. The main disadvantage of quartz is that it is rather expensive and more difficult to mechanically process than glass. It may be interesting to learn of the availability of quartz in mineral- rich countries of the FSU.

Transparent Conductors

Bell Labs' G.A. Thomas, who has made many contributions to the understanding of the metal-insulator transition, has said that he thought there were interesting open fundamental questions on electron transport mechanisms of indium tin oxide (Private Communication). ITO has no problems with handling low-resolution passive displays. So, it is not surprising that this issue was not yet discussed in the former Soviet Union, which has ITO production capability in Saratov. But this seems likely to become an important question for HDTV resolution displays (Footnote 17).

Backlight Technology

Backlight technology is still rather young in the FSU, where scientists are now concentrating on LCDs that do not use it. For example, it seems that the backlight in the avionic display is responsible for its cube-like appearance.

The panelists learned nothing about the high-speed dispersed particle technology. (For electrochromic materials used in emissive displays, see Phosphors and Other Emissive Materials; see Liquid Crystal and Other Nonemissive Displays for an evaluation of the state of FSU electronics to drive LCDs.)


Published: December 1994; WTEC Hyper-Librarian