Reliability of Liquid Crystal Display

This paper reports the reliability of twisted nematic liquid-crystal display for basic applications such as watches and calculators. We have studied significant stress factors such as voltage, temperature and humidity, and their corresponding failure modes. The main failure mode is LCD misalignment; many different modes appear corresponding to different stress conditions as well as material and process for the LCD. We have analyzed the accelerated test results by Weibull distribution, elucidated accelerating factors, and estimated life time. The life is inversely proportional to 1.78-2.45 power of applied voltage, depending upon misalignment modes. The distribution of life is well expressed by Weibull distribution with shape parameter between 2.5-3.0, and proportional to the square of coefficient of variation of life. We conclude that the acceleration factors could be determined and 99.9% of tested displays will live more than 10 years. The knowledge on reliability of LCD can be now applied to new fields of LCD, such as industrial use, home appliance, and automotive instruments.     

Mechanism of Misalignment Failure of Liquid-Crystal Display Cells

Misalignment properties and the misalignment generation mechanism due to voltage stress in liquid crystal display cells which use Schiff base-type liquid crystal were studied. Patterns of misalignment have many different modes, depending on the applied voltage. Based on the results of voltage-stress life tests and dismantling inspections of misaligned cells, we found that misalignment is due to the electrochemical deposition on the electrode surface of compounds formed of hydrolized components of the liquid crystal and inorganic impurity ions that have become mixed in during manufacturing, regardless of the visual patterns of misalignment.     

Radio-Frequency Coils in Implantable Devices: Misalignment Analysis and Design Procedure

Radio-frequency (RF) coils are used extensively in the design of implantable devices for transdermal power and data transmission. The practical issues of coil misalignments and configurations have not been investigated, and this paper presents a detailed theoretical analysis of misalignment effects in RF coil systems, including lateral and angular misalignments. Formulas are derived for the mutual inductance and, whenever possible, simplified upper bounds and lower bounds of the coupling coefficient are provided. A design procedure is established to maximize coil coupling for a given configuration, and a companion paper [1] discusses a circuit design technique to reduce the effects of misalignment on transmission efficiency.     

Increasing the speed of microstrip-line-type polymer-dispersed liquid-crystal loaded variable phase shifter

We discuss a method for the production of microwave polymer-dispersed liquid-crystal devices. We also show how to obtain a fine grained uniform fibrous polymer network. We then measure how the microwave-band dielectric properties and response-time characteristics of microstrip-line-type polymer-dispersed liquid-crystal devices vary with polymer concentration, and we measure how their response-time characteristics vary with the thickness of the polymer-dispersed liquid-crystal layer. With a layer thickness of 50 /spl mu/m, an applied voltage of 100 V and a polymer concentration of 7 wt%, we show that the decay time can be reduced to approximately 1/30th that of a plain liquid crystal at the expense of an increase in rise time of approximately 2.5 times and a deterioration of dielectric birefringence of approximately 50%. Finally, we discuss the results obtained with a prototype polymer-dispersed liquid-crystal loaded variable phase shifter in the 15-GHz band. By comparing the variable phase and response time of this phase shifter with basic experimental data obtained by the microwave resonance method, we verified the validity of these values.     

用高低温循环加速试验评估光源模块长期贮存寿命的研究

Light source modules are the most crucial and fragile devices that affect the life and reliability of the interferometric fiber optic gyroscope （IFOG）. While the light emitting chips were stable in most cases, the module packaging proved to be less satisfactory. In long-term storage or the working environment, the ambient temperature changes constantly and thus the packaging and coupling performance of light source modules are more likely to degrade slowly due to different materials with different coefficients of thermal expansion in the bonding interface. A constant temperature accelerated life test cannot evaluate the impact of temperature variation on the performance of a module package, so the temperature cycling accelerated life test was studied. The main failure mechanism affecting light source modules is package failure due to solder fatigue failure including a fiber coupling shift, loss of cooling efficiency and thermal resistor degradation, so the Norris-Landzberg model was used to model solder fatigue life and determine the activation energy related to solder fatigue failure mechanism. By analyzing the test data, activation energy was determined and then the mean life of light source modules in different storage environments with a continuously changing temperature was simulated, which has provided direct reference data for the storage life prediction of IFOG.     

Performance analysis by simulation of floating-gate MOSFETs applied on a bidirectional associative memory architecture

Floating-gate MOSFETs (FGMOSFETs) are devices that can be electrically programmable and have a non-volatile characteristic. This feature can be adopted to configure a basic cell performing as a variable resistance that can be applied in artificial neural networks as a synapse. Based on a simple model and considering the coupling coefficient of the structure as the gain of a voltage controlled voltage source, the electrical characteristics of a floating-gate MOSFET can be simulated in PSpice and an artificial neural net, such as the bidirectional associative memory (BAM), can be implemented. Therefore a performance analysis of the net may be done with different sets of threshold voltages for the FGMOSFETs configured as a CMOS inverter used as a synapse. The objective is to know pattern pairs in a bidirectional way. The result is a correlation matrix for the BAM as a function of an electrical parameter of the devices, which is directly related to the respective matrix calculated by the matrix dot product, using the method outlined by Kosko.     

A new technique for measuring coupling coefficients and 3-Dcapacitance characterization of floating-gate devices

The characteristics of the capacitance in floating-gate devices are comprehensively investigated. The capacitive coupling coefficient (α_c) between the control and floating gates is measured simultaneously, by a new technique, with the shift in threshold voltage during the programming. The present results are compared with those found from other methods and the dependence of α_c on applied voltages is examined. It is also shown that the α_c -data from a set of test patterns with varying floating-gate widths leads to the 3-D characterization of small geometry floating gate devices down to subfemto Farads. These measured characteristics are discussed in correlation with the effects of both the short channel length and of the narrow gate width     

The dependence of orientational optical nonlinearity in dye-doped liquid-crystal films on the polarization direction of the recording beams

We study, both experimentally and theoretically, the dependence of the absorbance and the two-beam coupling diffraction efficiency of dye-doped liquid-crystal films on the angle between the director vector of the liquid-crystal molecules and the polarization direction of the recording beams, which is shifted continuously from parallel to antiparallel corresponding to the director vector of the liquid-crystal molecules. The sample used in our experiment is the nematic liquid-crystal 5CB-doped with Disperse Red 1 (DR1). Also, there is no electronic field applied to it. The diffraction efficiency of the probe beam increases with the increase of the recording light absorption. Coupled-wave equations are developed to describe the laser-induced refractive index change, grating formation, and coherent wave-mixing effect. The analytical solutions of the recorded holographic grating and the diffraction efficiency of the probe beam are obtained for the case of taking losses into account. The results show that the diffraction efficiency can be improved by choosing suitable material parameters and recording parameters.     

Effects of dielectric anisotropy on DSM-type display devices

The transmission of dynamic-scattering-mode (DSM) liquid-crystal cells was studied as a function of dielectric anisotropy and surface alignment. Dielectric anisotropy of about -0.2 was found to be optimum for the devices from the viewpoints of threshold voltage, contrast ratio, and recovery time. Vertical-aligned cells were found to have higher contrast ratios and longer recovery times than parallel-aligned cells.     

4×4纵横交换微电机械系统光开关阵列

微电机械系统(MEMS)光开关是微电机系统技术与传统光学技术相结合的新型机械式光开关。采用纵横交换网络和通断型微镜实现4×4微电机械系统光开关阵列,利用球透镜单模光纤准直器作为微电机械系统光开关阵列的输入、输出端口。运用高斯光束耦合理论对光开关阵列插入损耗(IL)进行了理论计算,并对引起插入损耗的主要因素进行了分析。对于失调容限:输入与输出光纤准直器位置失调2μm,定位角度失调0.15°,微镜非垂直反射角度失调0.15°,制作了4×4微电机械系统光开关阵列,对其各个通道的插入损耗进行了实验测试,其中最大值为2.77dB。     

Low-Voltage Magnetoelectric Coupling in Fe0.5Rh0.5/0.68PbMg1/3Nb2/3O3-0.32PbTiO3 Thin-Film Heterostructures

The rapid development of computing applications demands novel low-energy consumption devices for information processing. Among various candidates, magnetoelectric heterostructures hold promise for meeting the required voltage and power goals. Here, a route to low-voltage control of magnetism in 30 nm Fe_0.5Rh_0.5/100 nm 0.68PbMg_1/3Nb_2/3O₃-0.32PbTiO₃ (PMN-PT) heterostructures is demonstrated wherein the magnetoelectric coupling is achieved via strain-induced changes in the Fe_0.5Rh_0.5 mediated by voltages applied to the PMN-PT. We describe approaches to achieve high-quality, epitaxial growth of Fe_0.5Rh_0.5 on the PMN-PT films and, a methodology to probe and quantify magnetoelectric coupling in small thin-film devices via studies of the anomalous Hall effect. By comparing the spin-flop field change induced by temperature and external voltage, the magnetoelectric coupling coefficient is estimated to reach ≈7 × 10⁻⁸ s m⁻¹ at 325 K while applying a −0.75 V bias.     

使用液晶微透镜的高分辨率三维重建双模相机

提出了一种基于液晶微透镜阵列的双模成像相机。该相机通过打开或者关闭加载在液晶微透镜阵列上的低频电压信号可以快捷地在传统平面成像模式和光场成像模式之间进行切换。液晶微透镜阵列通过常规紫外光刻和湿法刻蚀技术制作而成。通过将液晶微透镜阵列和感光传感器阵列以及主镜头耦合到一起,构造了一个双模成像相机的原型。通过该双模成像相机开展了相关实验,获取了同一目标物的光场图像和平面图像,并对孔径设计和两种工作模式下的景深进行了分析,给出了光场成像模式下目标物三维信息的计算方法,通过将三维光场数据和对应二维平面数据的信息进行融合获得了高分辨率三维图像。     

A design of multiplexing liquid-crystal display for calculators

A numeric liquid-crystal display using the dynamic scattering mode has been developed for calculators by adopting a total system design through the integrated development of material, device, and system. A mixed Schiff-base nematic liquid crystal with the dopants of l-hexadecylpyridinum bromide and p-aminophenol has been developed for the 1:2 selection multiplexing drive over a wide temperature range (0-40°C). A reliable package has been achieved with new technology. A 1-chip CMOS driving circuit with a 42-lead package has been developed for 8-digit 7-segment numeric readout displays in order to eliminate the dc component of the applied voltage, to minimize variations in the drive voltage, and to reduce power consumption. The devices have passed severe reliability tests. Our displays have lasted 15 000 h under normal test conditions. Using the dichroic mirror approach, it has become possible to design color displays of yellow, green, blue, or any color which have high readability and wide viewing angle under severe ambient light conditions.     

In-process voltage stressing to increase reliability of MOS integrated circuits

Time-dependent dielectric breakdown of gate oxides is one of the principal failure mechanisms of MOS integrated circuits. Voltage stressing of completed devices, which has been used to screen oxide defects and to thereby increase product reliability, is less effective with scaled high-density MOS integrated circuits because of limitations in the voltage which can be applied. Inprocess voltage stressing of silicon wafers, prior to completion of wafer processing, offers a feasible technique for achieving an effective voltage screen. Several possible techniques for inprocess voltage stressing are described, and the advantages and limitations of these are outlined. Data are presented showing typical fast-ramp dielectric breakdown distributions for MOS transistor arrays with an oxide thickness of 35 and 50 nm. Time-dependent dielectric breakdown distribution data on devices from the same wafers indicate that with all MOS transistors of an integrated circuit connected in parallel, as in one type of inprocess voltage stressing, defective oxide sites can be screened in periods of time ranging from a few seconds to hours. Inprocess voltage stressing, by decreasing susceptibility of completed devices to time-dependent dielectric breakdown, can substantially increase MOS integrated circuit reliability.     

腔失调对模耦合的影响

综合分析了腔失配和腔失调对模耦合的影响，分别讨论了模的功率耦合系数与失配参量、失调位移及失调角的相互关系。     

Linear 0.20 GHz modulation with a 1×2 directional coupler

The design and performance of a traveling-wave 1×2 directional coupler modulator are described. A 0-20 GHz response (-4 dB _e) was achieved for Ti:LiNbO₃ devices at the 1.3-μm wavelength. From experimental determinations of coupling coefficient and interarm intrinsic phase-mismatch for several modulators, linear dynamic ranges of, on average, 78 dB and voltage sensitivities of down to 9 μV are determined (for 1-mW detector power, 3-kHz bandwidth, 50-Ω detector load). The dependence of sensitivity on the coupling coefficient is described, and the effect of the buffer layer thickness on the optical bandwidth and sensitivity is demonstrated     

Novel coupled-line conductor-backed coplanar and microstrip directional couplers for PCB and LTCC applications

Novel coupled-line conductor-backed coplanar and microstrip directional couplers, convenient for manufacturing in standard printed circuit board (PCB) or low-temperature co-fired ceramic (LTCC) technology, are proposed. The coplanar coupler, consisting of a layered structure with four strips and covering a -10 to -2.6 dB coupling coefficient, is theoretically ideally impedance matched and perfectly isolated at all frequencies under the assumption of validity of quasi-static approximation and two-mode propagation. The microstrip coupler, a modification of the coplanar one, can be ideally compensated only in an area of strong coupling coefficients. The novel couplers are not sensitive to lateral misalignment of conductive layers, and not sensitive to thickness and dielectric permittivity tolerances of applied dielectric substrates. Preliminary experimental results for 2.7-, 3-, and 8.34-dB couplers, designed both in PCB, as well as LTCC technology are presented.     

Enhancing the efficiency of alternating current driven organic light-emitting devices by optimizing the operation frequency

We report efficient and bright organic light-emitting devices operated by capacitive energy coupling. In this approach, the organic layers are enclosed between sputter-deposited hafnium dioxide layers to prevent charge carrier injection. When a sinusoidal voltage signal is applied to the electrodes, the devices emit bright green light whereas no detectable emission is generated upon application of a constant voltage. The efficiency of the process depends heavily on the frequency of the applied voltage signal. By optimizing the driving scheme, a record luminous efficacy for AC driven OLEDs of 2.7 lm/W at 500 cd/m² is achieved.     

Reliability problems in TTL-LS devices

An analysis of the possible failure modes of TTL-LS was carried out, with particular emphasis on long term thermal stability of Schottky diodes, all realized by PtSi - Ti/W - Al metallization system.Only from one supplier were there diodes in which changes in the characteristics, due to metallization defects, were observed during accelerated thermal cycles. On the contrary, once its uniformity is guaranteed, the Ti/W barrier layer inhibits the Si-Al interdiffusion up to 550 °C, 1 hr thermal annealing.Sensitivity to negative input pulses and electrical overstresses were also investigated.Scanning electron microscope and microprobe, and voltage contrast techniques seem to be more suitable instruments to investigate the reliability of such devices than the conventional life tests.The technology employed today seems provide suitable reliability for TTL Low-Power Schottky devices.     

Liquid-crystal display prospects in perspective

The advantages of dynamic scattering liquid-crystal displays--extremely low power consumption, flexibility of size and format, color choice, and washout immunity--are not obtained without cost. Long life requires ac drive and hermetic packaging. The optical characteristics of dynamic scattering make it difficult to design a display that utilizes the liquid-crystal panel effectively under a variety of lighting conditions. Multiplexed drive is cumbersome at best, so cost of drive electronics for more than about four digits is higher than with competing display technologies. The development of twisted nematic displays will reduce drive costs and improve appearance although the changes will not be revolutionary. The large multiplexing capability or color variability of the alterable birefringence effect is offset by prohibitive manufacturing tolerances and narrow field of view. Led by low-power digital wristwatches, liquid crystals should achieve a substantial market in applications whose requirements match unique display properties. Effective penetration of the consumer mass market will await improved field-effect devices and reductions in semiconductor packaging costs.