Processes,characterizations, and system applications of color‐filter liquid‐crystal‐on‐silicon microdisplays

Abstract— A color‐filter liquid‐crystal‐on‐silicon (CF‐LCOS) microdisplay that integrates color filters on silicon for color will be presented. The color‐filter process on silicon was optimized to achieve fine resolution and precise alignment of the color filters on the pixel array, good adhesion to the silicon suface, and a flat surface for the liquid‐crystal cell assembly. Important optical and electrical parameters of the color filters were extracted to establish an electro‐optical model of the CF‐LCOS microdisplays for device simulation. Thermal, chemical, and light‐stability characterizations were performed to ensure the stabilty of the color filters and CF‐LCOS microdisplays. With color CF‐LCOS microdisplays already available, the projection or viewing optics is greatly simplified. This CF‐LCOS microdisplay is ideal for near‐to‐eye displays because of its low‐power consumption and compactness. The CF‐LCOS microdisplay could also withstand medium light illumination for medium‐sized projectors. A single‐panel projector based on one CF‐LCOS microdisplay of 1280 × 768 × RGB resolution was demonstrated.     

Optimization of photo‐aligned ferroelectric liquid‐crystal display under passively addressed driving

Abstract— A ferroelectric liquid‐crystal (FLC) passively addressed 64 × 64 display based on the photo‐alignment technique has been developed. The display matrix has dimensions of 33 × 33 mm², and the FLC layer thickness is about 5 μm. Asymmetric boundary conditions, when only one of ITO surfaces of the display matrix is covered with the photo‐aligning layer while another one is not, have been used for providing both high contrast ratio and steady multiplex operation. The electro‐optical performance of the 5‐μm FLC display is presented, including bistable switching in static operation, optimization in multiplexing operation, and gray‐scale generation.     

Contrast optimization for MacNeille‐PBS‐based LCOS projection systems

Abstract— Contrast limits are investigated for MacNeille‐PBS‐based LCOS projection systems that use retarder stack filters (RSFs). The two contributing factors are considered separately; namely, the color‐management system and the panel port. To enhance performance of the former, skew‐ray‐compensated RSFs are introduced. For the latter, a general three‐step methodology is presented to optimize contrast by compensating the LCOS panel. It is shown that the orientation of the LCOS panel and compensator, relative to the MacNeille PBS, is critical. The significant impact of AR‐coating performance on system contrast is also revealed. Methods to enhance ANSI contrast are proposed. A high‐contrast architecture will be presented by way of example.     

Pre‐tilt angle and cell‐gap measurement of vertically aligned non‐twisted liquid‐crystal displays

Abstract— A measurement method for the determination of the cell parameters of vertically aligned nematic LCOS devices has been developed. It provides the values for the pre‐tilt angle and the cell thickness in a reliable way, without the need for spectroscopic instruments. The method uses oblique incidence to separate the determination of pre‐tilt angle and cell thickness from each other and thus enhance the measurement accuracy. As a bonus, the measurement system consists only of simple optical components and does not need costly instruments.     

Microdisplay‐based optical module for avionic display applications

Abstract— A new optical scheme for a LCOS‐based rear‐projection system utilizing an LED illumination source is presented. The proposed optical module could conveniently replace conventional aircraft panel instrumentation not only because it achieves major standard avionics application requirements, such as the capability to withstand mechanical shocks, high reliability, and weight and power‐consumption minimization, but also as a consequence of the fact that it allows the display image area to be properly matched to the shape of the instrument panel more easily than with conventional displays.     

A miniature coupled‐line‐based 3‐dB directional coupler using GaAs PHEMT process

A novel complementary‐conducting‐strip (CCS) coupled‐line (CL) design is proposed to achieve compact size by applying two‐dimensional layout and standard gallium‐arsenide (GaAs) thin‐film technology. To obtain high coupling and satisfy the design rules of GaAs process, mixed‐couple mechanism with edge and broadside coupling are also used. A CCS CL‐based Ka‐band 3‐dB directional coupler is fabricated using WIN 0.15‐μm GaAs pseudomorphic high electron mobility transistor technology. Experimental results show that the proposed directional coupler can cover the entire Ka‐band (26–40 GHz) with through and coupling of approximately 3.7 ± 0.25 dB, and isolation of better than 13 dB. In addition, the phase difference between the two output ports is approximately 90° ± 5°. The occupied area of the prototype (without I/O networks) is only 220 × 220 μm². © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:21–26, 2016.     

Single‐cell‐gap transflective liquid‐crystal display using double‐ and single‐mode approaches

Abstract— In this paper, many popular methods to study transflective liquid‐crystal‐displays (LCDs) have been discussed, and several new transflective LCD configurations with a single‐cell gap have been proposed. The traditional double‐cell‐gap method gives the best match of the transmittance/reflectance voltage curve (TVC/RVC) and also the widest viewing angle, but also brings the highest fabrication complexity. The single‐cell‐gap transflective LCD is much easier to fabricate and also shows a good match of TVC/RVC. A new methodology has been shown to find optimal configurations for single‐cell‐gap transflective LCDs. New configurations using multimode in a single pixel include twisted nematic (TN) optically compensated bend (OCB), TN electrically controlled birefringence (ECB), and TN low‐twisted nematic (LTN). TN and hybrid‐aligned nematic (HAN) modes have been investigated for single‐mode transflective LCDs. The results exhibit high contrast ratio, a good match of TVC/RVC, as well as wide viewing angle.     

Diamond‐like‐carbon LC‐alignment layers for application in LCOS microdisplays

Abstract— To improve the lifetime and yield of LCOS microdisplays, non‐contact LC alignment techniques using inorganic materials are under investigation. This report focuses on oblique ion‐beam treatment of diamond‐like carbon (DLC) layers, and in particular on the influence of the ion dose on the LC alignment on DLC, keeping the ion‐beam angle (40°) and ion‐beam energy (170 eV) the same. LC alignment on ion‐milled DLC layers is uniform if the ion dose is between 3.8 × 10^?4 C/cm² and 5.5 × 10^?3 C/cm². Above and below this ion dose range, non‐uniform alignment is observed. NEXAFS experiments show that this is caused by lack of molecular anisotropy on the surface of the ion‐milled DLC layers. By varying the ion dose between 3.8 × 10^?4 C/cm² and 5.5 × 10^?3 C/cm², LC molecules have an average pre‐tilt between 3° and 5°, which is within the desired range for application in LCOS microdisplays. The lifetime of the LCOS microdisplays with ion‐milled DLC for projection‐TV application is, however, shorter than the lifetime of microdisplays with PI layers. Ion milling probably creates a reactive surface that is unstable under the high light fluxes used in projection TVs. A solution for this problem could be chemical passivation of the ion‐milled alignment layers. Initial experiments with passivation of ion‐milled PI resulted in an increase in lifetime, but the lifetime after passivation was still lower than the lifetime of rubbed PI layers (factor 0.7). Nevertheless, ion‐milling of DLC or PI can be a good alternative LC alignment technique in other LCD applications. LC‐alignment layers based on inorganic layers such as obliquely deposited SiO₂ films would be a better option for application in LCOS microdisplays due to their higher light stability.     

Wire‐grid polarizers in modern LCOS light‐engine configurations

Abstract— Wire‐grid polarizers that have a very high transmission, reflection, polarized‐light optical performance, and opto‐mechanical packaging advantages compared to the older polarization technologies have been developed. The wire‐grid polarizer operation principles and performance data are reviewed. The power of using finite‐difference time‐domain (FDTD) modeling techniques to understand the interaction of the electromagnetic waves with the wires and improve the optical performance of the wire‐grid polarizers and ultimately the light‐engine optical performance is shown. The ability to ray trace through a complete digital projector light engine from light source to the screen, including the wire‐grid polarizers, will be discussed. The main focus is to present the modern LCOS light‐engine architectures that use the wire‐grid polarizers. One‐, two‐, and three‐panel LCOS light engines are covered.     

A silicon‐chip‐based light valve with reflective twisted‐nematic mode for high‐definition projectors

Crystalline‐silicon‐chip‐based reflective light valves are suitable for realizing high definition and bright liquid‐crystal projectors. We have developed an XGA (1025 × 769 pixels) silicon‐chip‐based light valve with a diagonal display area of 2.54 cm (1 in.). The reflective twisted‐nematic mode was examined by using the Jones matrix method as a display mode, and the normally white reflective twisted‐nematic mode was selected. This mode is suitable for a narrow cell gap, and a fast response time can be expected. In addition, the driving voltage of this mode is low and has good chromaticity with small retardation. The cell gap of the light valve is 2 μm. The cell gap support is made using spacer posts formed on the silicon chip with a photodefinable resin. The response time is 12 msec, including both rise and fall times. The contrast ratio is more than 1000 at 5 Vrms.     

Toward sub‐micron oxide thin‐film transistors for digital holography

High‐performance 2‐μm‐channel oxide thin‐film transistors (TFT) on glass substrate for a 7‐μm‐pixel‐pitch spatial light modulator panel for digital holography applications were fabricated using a two‐step source/drain etching process. It showed a μ_FE of 45.5 cm²/Vs, SS of 0.10 V/dec, and Von of near zero voltage. Furthermore, we succeeded in the demonstration of sub‐micron TFTs, which is an indispensable route to next‐generation spatial light modulation devices with near 1‐μm pixel pitch. The issue of short‐channel transistors for display applications is also introduced. Finally, the digital holographic demonstration results based on the fabricated backplane are presented.     

Three‐panel LCOS projection systems

Abstract— Three‐panel liquid‐crystal‐on‐silicon (LCOS) projection systems are presented with an emphasis on the commercially successful shared retarder‐stack‐filter (RSF) polarizing‐beam‐splitter (PBS) architectures. The design and operation of the specific CQ90 projection core is presented in detail, and its contrast and transmission derived. alternative three‐PBS/X‐cube LCOS architectures are briefly introduced and their performance is compared to that of the CQ90.     

Transflective TFT‐LCDs with high optical performance

Abstract— In order to reduce panel cost, reduce power consumption, and minimize thickness, a single panel with dual functions for high‐transmissive main displays and high reflective sub‐displays is becoming the trend. Two novel RGB‐W transflective 1.9‐in. a‐Si TFT LCDs have been developed to meet the requirements. By using the traditional seven‐mask dual‐cell‐gap structure, novel transflective tRGB‐t/rW TFT LCD and tRGB‐rW TFT‐LCD panels were fabricated with high transmittance and high reflectance, respectively. The optical clarity is excellent in both dark and bright conditions. Their superior optical performance is attributed to the high‐efficiency “transflective white” subpixel or “reflective white” subpixel.     

Magnetically inert medical projection system with an image‐guiding optical fiber

Abstract— A visual system for stimulating specific human brain functions inside a clinical magnetoencephalography (MEG) measurement chamber was developed. This system is based on a three‐panel LCOS projection unit and uses a 4.5‐m‐long image‐guiding optical‐fiber bundle to transfer the image into the magnetically shielded MEG measurement chamber. In addition to a proper optical system design, special attention had to be paid to all materials used inside the magnetically shielded chamber. Here, no interfering fields due to electrics or ferromagnetic materials are allowed. The system concept, optical design, and the realized prototype are presented.     

Switchable transmissive and reflective liquid‐crystal display using a multi‐domain vertical alignment

Abstract— A wide‐view transflective liquid‐crystal display (LCD) capable of switching between transmissive and reflective modes in response to different ambient‐light conditions is proposed. This transflective LCD adopts a single‐cell‐gap multi‐domain vertical‐alignment (MVA) cell that exhibits high contrast ratio, wide‐viewing angle, and good light transmittance (T) and reflectance (R). Under proper cell optimization, a good match between the VT and VR curves can also be obtained for single‐gamma‐curve driving.     

Comparison of some characteristics of thin‐film‐electroluminescent ZnS: Er,F planar and edge emitters

Abstract— The following main differences have been revealed in the characteristics of an edge thin‐film‐electroluminescent ZnS: Er,F emitter compared to those of a similar planar emitter: (1) the 1.535‐μm band more highly dominates over other bands in the EL spectrum; (2) the voltage (V) dependence of the intensity of this band is the strongest; (3) the 1.535‐μm band narrows with increasing voltage and its frequency. The above differences are explained, firstly, by smaller optical losses in the ZnS: Er,F film for the near‐infrared emission than for the visible one and, secondly, by an optical amplification over the 1.535‐μm band in the edge emitter.     

Viewing‐angle‐switching device based on array of optical micro‐rods incorporated with electrophoretic material systems

We have successfully demonstrated a control device for a viewing angle that enables switching between two states, a wide‐viewing angle, and a narrow‐viewing angle. It is composed of a light‐transmitting portion formed with an array of optical micro‐rods and a shielding/transmitting changeable portion of cross stripes designed with electrophoretic material systems consisting of black particles and an optically transparent medium. When the black particles are fully dispersed in the optically transparent medium, the cross stripe portion plays the role of a non‐transmitting material as the shielding portion in a similar manner to a conventional viewing angle control film. When the black particles are completely gathered electronically to one side in the optically transparent medium, in contrast, the cross stripe portion filled by the optically transparent medium can transmit incident light. These functions allow us to select electrically either of two modes between a limited viewing angle and a non‐limited viewing angle. The optical properties for the limited viewing angle mode were +/?30° of the visible angle and 50% of the transmittance, and the one for the non‐limited viewing mode was 58% of the transmittance. The response time from the narrow‐viewing angle to wide‐viewing angle was 1 s at 20 V of applied voltage.     

Novel application of ink‐jet‐printing technology in multi‐domain alignment liquid‐crystal displays

Abstract— Based on the drop‐on‐demand characteristics of ink‐jet printing, the multi‐domain alignment liquid‐crystal display (LCD) could be achieved by using patterned polyimide materials. These polyimide ink locations with different alignment procedures could be defined in a single pixel, depending on the designer 's setting. In this paper, we combined the electro‐optical design, polyimide ink formulation, and ink‐jetting technology to demonstrate the application of multi‐domain alignment liquid‐crystal display manufactory. The first one was a multi‐domain vertical‐alignment LCD. After the horizontal alignment material pattern on the vertical alignment film, the viewing angle would reach 150° without compensation film. The second one was a single‐cell‐gap transflective LCD within integrating the horizontal alignment in the transmissive region and hybrid alignment in the reflective one in the same pixel. In addition, this transflective LCD was also demonstrated in the form of a 2.4‐in. 170‐ppi prototype.     

Optimization of contrast for MTN45 LCOS panel

Abstract— MTN45 LCOS was studied experimentally and by simulation. Optimized retardance and orientation of the compensation retarder were found by simulation and verified by experimental data for both wire‐grid PBS and McNeil‐type PBS systems. The parasitic reflectance from the counter‐electrode (CE) glass and the retarder surface are two major effects that decrease the contrast of LCOS panels. Their effect was simulated by inserting several imaginary optical layers into the real system. Results also show that decreasing the retardance of the retarder; thus increasing the maximum driving voltage for the dark state can increase contrast. By combining all the improvements, we can achieve a contrast of 1500:1 in green and a contrast of 1000:1 in blue for MTN45 LCOS panels.     

Compact and power‐saving polysilicon data driver with common‐decoder DA converter (CD‐DAC)

Abstract— A common‐decoder architecture for a data‐driver circuit fabricated by using a polysilicon process has been developed. The architecture achieves a compact circuit and low‐power consumption. In application to an integrated polysilicon data driver for small‐sized displays, this architecture reduces the area of the data driver by removing the vertical bus lines that occupy a large area. It also suppresses the power consumption of the data bus by reducing the number of driven lines in the data bus during word‐to‐word transitions from six to two. By using a conventional 4‐μm design rule, we fabricated an active‐matrix OLED (AMOLED) panel with an integrated six‐bit data‐driver circuit with 384 outputs. The driver circuit had a height of 2.6 mm and a pitch between output lines of 84 μm. The maximum power consumption of the driver was only 5 mW, i.e., 3.8 mW for logic‐data transfer and 1.2 mW for reference‐voltage source. Furthermore, we also fabricated an active‐matrix LCD (AMLCD) panel including driver circuits of the same type as the integrated elements. Six‐bit full‐color images were successfully displayed on both panels.