Site: Institute of Physics of Semiconductors
Ukraine Academy of Sciences
252650 Kyyiv, pr. Nauky, 41
Ukraine

Date Visited: October 26, 1993

Report Author: O.D. Lavrentovich

ATTENDEES

WTEC:

M.J. DeHaemer
O.D. Lavrentovich

HOSTS:

Sergiy Vasyl'ovych Svechnikov

Victor Mykhailovych Sorikin

BACKGROUND

The Institute of Semiconductors was established in 1960 based on some divisions and laboratories inherited from the Institute of Physics. The institute is composed of seven departments performing research and development in photoelectronics, semiconductors, physics of liquid crystals, and microelectronics. The departments comprise twenty-five divisions and twenty-four laboratories. On January 1, 1993, the institute became the Institute of Physics of Semiconductors.

RESEARCH AND DEVELOPMENT ACTIVITIES

Laboratory of Liquid Crystals

(Head: Prof. Viktor M. Sorokin)

Research and development of different electro-optical effects in LC includes: (a) development of new technologies of LC orientation; (b) new materials and effects for display application; and (c) characterization facilities.

Liquid crystal orientation. The laboratory has equipment that includes units for magnetron sputtering, electron beam evaporation, thermoevaporation, reactive cathode deposition (cathode diameter 220 mm), ionic treatment, and laser interference control of a film thickness. The productivity of the line is 200 cm²/hr for the ITO coating. The laboratory has developed a three-stage method of alignment: (1) ITO deposition by magnetic mask; (2) magnetron sputtering of SiO₂ (or similar materials such as NiO, TiO); and (3) cathode sputtering of orienting microrelief (Sorokin et al. 1992a). The control of the angle of the cathode sputtering allows one to control the pretilt angle in the range from 0-30þ. The method permits creation of two easy directions in the plane of the substrate, thus obtaining a bistable electro-optical nematic device. An external electric field switches the two states of the LC orientation. This work is performed in collaboration with Professor G. Durand's group (Laboratoire de Physique des Solides, Universite de Paris-Sud, Orsay, France).

New Materials and Effects:

Cholesteric display. In collaboration with the Monocrystal Institute in Kharkiv (Prof. O. Gerasimov) and the Institute of Physics (Prof. V. Nazarenko and Prof. V. Sergan), the LC Laboratory is developing a cholesteric-based display. The working material is composed of a nematic LC doped with optically active (chiral) substance. The composition was proposed in Kharkiv (Prof. Gerasimov); the electro-optical properties are studied in Kyyiv (Drs. Sorokin and Nazarenko). Under the action of the electric field, the cholesteric structure reorients. The resulting textures depend on the applied voltage U and the switch-off time:

1. U < U_th Initial planar texture transforms into a focal conic scattering texture that remains stable after a fast voltage switch-off;
   
2. U > U_th The cholesteric structure transforms into the nematic untwisted structure. The switch-off leads either to the focal conic texture (if ç > ç_th) or to the planar texture; if (ç < ç_th) the display shows a color transition from black to bright green (Sorkin 1992a; Gerasimov 1993a, 1993b; Sorokin 1992b; Oleksenko 1993).

A similar technology was proposed and developed earlier at the Liquid Crystal Institute, Kent State University (Drs. J.W. Doane and D.K. Yang). The difference is that in the Ukrainian method, the LC is doped with low-molecular chiral substance, while the Doane-Yang method uses a polymeric gel in combination with cholesteric mixture. The Ukrainian physicists claim response time of approximately 1 ms, coefficient of the light reflection 0.46-0.48.

Effect of the total internal reflection. The laboratory develops biprismatic-nematic modulators operating by the electric field. The field changes the director orientation and, consequently, an effective refractive index. The system is designed to satisfy the condition of the total internal reflection for a particular field threshold. The device can be used in photocopy machines.

Characterization Facilities:

Special automatically-controlled characterization facilities have been developed to measure parameters of LC displays: contrast ratio, switch time, intensity versus view angle, threshold voltage, gray scale, etc.).

Department of Optoelectronics

(Head: Academician Sergiy Vasylyovych Svechnikov)

The WTEC team met with Professor S.V. Svechnikov, who is the head of the institute and head of the department. The principal trends of research in the field of displays performed in the department were discussed:

1. Thin-film EL structures based on ZnS, ZnSe, ZnSMn, and so forth, are under development. Colors: yellow orange, red, green, and blue. Recently a new type of EL indicator has been developed that operates on the basis of integrating the thin-film and luminescent structure and the active layers of ferroelectric ceramics. Another trend is the manufacturing of two-colored matrix screen on glass and ceramic substrates.
2. Electrochromic materials (such as tungsten oxides) are being investigated and developed.
3. Light-emitting structures and photodetectors based on III-V semiconductors are another trend. The amorphous SiC structures deposited onto flexible substrates have been developed recently.
4. With powder luminescence, the problem is to organize manufacturing of the powder-luminescence indicators and screens rather than performing investigations. The corresponding large screen was manufactured in Mukachevo (West Ukraine); it works, but the performance is poor.
5. With regard to laser TV, the institute develops materials for the projection TV screen. Each element of the screen is composed of a small crystal, which works as a laser source.
   

DISCUSSION

Q. When will large EL TV screens be available?
A. The largest EL TV screen will have a size ~20 x 30 cm². The problem is that the EL screens are high-powered devices; the LCDs have advantages as low-power and easily operated devices.

Q. What is your vision of the future of the institute?
A. The institute has a broad profile of R&D (including semiconductors II-V, II-VI, organic semiconductors, Si, high-temperature superconductivity, condensed matter theory, porous materials, and so forth). The ratio of the fundamental to the applied studies is 1:1. The absence of adequate financial support creates problems. It will be necessary to cut some investigations and to concentrate only on priority R&D.

SUMMARY

The Institute of Semiconductors performs first-class R&D in the field of LCD and ELD. Scientific finding can be developed and can result in the manufacturing of displays (e.g., cholesteric-based LCDs). The manufacturing can be organized within Ukraine (e.g., in collaboration with the Institute of Microelectronics, Korolyov Industrial Complex, Kyyiv, and with Zhovten, Vinnutsya).

REFERENCES

Gerasimov, A.A. 1993a. "Electro-Optical Behavior of the Cholesteric-Nematic Mixtures Within the Visible Light Region," European Conference on LC, Basel.

Gerasimov, A.A., Yu. P. Burmistrov, V.M. Sorokin, and V.V. Sergan. 1993b. "Large Size Front-Lit Panels of LC Display Based on the Cholesteric-Nematic Mixtures." European Conference on LC, Basel.

Oleksenko, P.F., and V.M. Sorokin. 1993. "Scientific and Technological Aspects of New LCD Technologies." International Conference on Physics in Ukraine, Kyyiv:207-211.

Sorokin, V.M., P.F. Oleksenko, Y.V. Kolomzarov, and R.Y. Zelinski. 1992a. "Investigation of Methods for Molecular Alignment in Nematic and Smectic Liquid Crystal Displays." Mol. Cryst. Liq. Cryst. 215:137.

Sorokin, V.M., A.G. Smirnov, and V. Vysotsky. 1992b. "Optimization of Half-Tone Image on MIM Addressed LCD's." Japan Display. 92:459-460.