Vacuum Fluorescent Display Research Articles

A life extrapolation model using accelerated equivalent luminance and its application

Aiming at predicting the life of vacuum fluorescent display (VFD) accurately, four groups of constant-stress accelerated degradation tests (ADTs) were conducted, and the life extrapolation model of accelerated equivalent luminance (LEMAEL) based on each test sample was proposed. In this model, firstly, Weibull function was employed to fit luminance degradation data of each sample at each stress. Secondly, Logistic function was determined by Anderson-Darling test to respectively describe the distributions of shape and scale parameters, and the degradation formula of accelerated equivalent luminance was obtained to estimate accelerated life. Finally, Power function was selected by comparing determination coefficients to fit the data points formed by accelerated life and stress, and thereby VFD life was extrapolated. The results indicate that the collected test data of each sample objectively reflect VFD luminance characteristics; the degradation formula intuitively exhibits the luminance variation law at each accelerated stress, and Power function accurately reveals the relationship between life and stress; LEMAEL is characterized by high precision and large amount of data information, which not only actualizes the accurate life estimation for light-emitting devices without conventional life tests, but also provides entirely new modeling ideas and thoughts for reliability evaluation and life prediction of products.

A Life Prediction Model for High-Reliability Products and Its Application to VFD Based on Constant-Stress ADTs

Abstract For many high-reliability and long-life products, the accuracies of some existing life prediction models are not high enough, which may limit their fast development. For this purpose, four groups of constant-stress accelerated degradation tests (ADTs) were carried out by increasing the temperature of a vacuum fluorescent display (VFD) cathodic filament, and the equivalent average luminance degradation model (EALDM) was proposed to predict VFD life. In this model, firstly, a two-parameter Weibull function was used to fit average test data at each accelerated stress, and the corresponding formula of luminance degradation was obtained. Secondly, a power function was determined to fit multi-groups of data points formed by an accelerated stress and time at different given luminance, and then the work time under normal stress was extrapolated. Finally, by reusing the Weibull function to fit the data points, including the work time and given luminance, the life prediction of products was achieved. The results indicate that the test design of constant-stress ADTs is correct and feasible; the Weibull function well reveals the VFD luminance decaying law at both accelerated and normal stresses, and the power function objectively reflects the relationship between work time and stress. It is found by comparing the predicted life with the reference value that EALDM has high precision, which paves the way for following research in life prediction methodology and acts as a guide for professional technicians.

Two life prediction models for optoelectronic displays without conventional life tests.

To precisely predict the life of optoelectronic displays over a short time, two life prediction models were established based on the three-parameter Weibull right approximation method (TPWRAM). In Model I, the acceleration life under each stress was obtained using TPWRAM, the data points formed by acceleration life and acceleration stress were, respectively, fitted by three extrapolation functions and the optimal extrapolation function was determined by comparing the fitting determination coefficient and root-mean-square error. In Model II, after introducing an acceleration parameter, the luminance attenuation data under conventional stress were calculated directly by combining the ones obtained using TPWRAM under each acceleration stress. The luminance attenuation test data from the vacuum fluorescent display (VFD) were collected through four groups of constant-stress accelerated degradation tests (ADT), and the two models were applied to the life prediction of VFD. The results indicated that the designed ADT scheme was feasible, Model I revealed the changing law of life with stress and simplified the process of life prediction, and Model II made it possible to obtain the luminance attenuation formula at conventional stress without conducting a conventional life test, overcoming the shortcomings of long time-consuming traditional life tests. It was verified by comparing the life prediction values that the two models had very high precision, and both of these not only achieve the accurate estimation of optoelectronic product life without resorting to conventional life test, but also improved the method of life prediction and perfect its theoretical system.

Reliability modeling for a two-phase degradation system with a change point based on a Wiener process

A two-phase degradation system with a change point is commonly seen in many real-world degradation systems due to influence of internal mechanisms and external environments, such as lithium-ion batteries, light-emitting diodes (LEDs), plasma display panels (PDPs), and vacuum fluorescent displays (VFDs). Random jumps exist at the change points of the degradation processes. Motivated by this phenomenon, this paper attempts to model such kinds of systems based on the Wiener process. Specifically, In Model 1, a constant change point model is first considered. The analytical results of the system reliability, lifetime distribution, and the remaining useful lifetime (RUL) are obtained. Then, based on Model 1, a random change point model, i.e., Model 2, is proposed to explain the change point phenomenon which is influenced by the accumulative effect of a shock process. Two phase-change patterns (PCPs) are considered in Model 2. For PCP I, the change point is triggered when the number of shocks reaches a predetermined threshold. For PCP II, the change point is triggered when the accumulative shock damage exceeds the corresponding threshold. The system reliability indexes are studied by using analytical and simulation methods. Finally, several numerical examples are given to illustrate the approaches and results.

Two optimized models of life prediction based on luminance degradation for VFD under a conventional life test

AbstractFocusing on improving the accuracy of existing life prediction models for optoelectronic products, the three‐parameter Weibull right approximation method (TPWRAM) was employed to substitute exponential function based on the least square method in the analysis and two‐staged methods. Two optimized models were established (Model I and Model II), based on maximum likelihood estimation and the Monte Carlo method, respectively. One group of conventional life tests (CLTs) of vacuum fluorescent display (VFD) were conducted to collect luminance degradation data for each sample, and the two optimized models were applied to achieve VFD life prediction and obtain mean time to failure, median life, and confidence intervals. The results indicate that the CLT test design is correct and feasible, the amount of data on luminance degradation is large, and the test data selection method is reasonable. Model I and Model II optimized by TPWRAM both reflect the VFD luminance variation law well, and the predicted life approaches VFD service life from user feedback, proving that the two models are precise, and thus, can provide technical references for researchers and engineers regarding aspects of life prediction.

A Comparative Study on R&D Organizations in Specialized Manufacturer and Generalized Manufacturer: A Case Analysis in the Vacuum Fluorescent Display Industry

A Comparative Study on R&D Organizations in Specialized Manufacturer and Generalized Manufacturer: A Case Analysis in the Vacuum Fluorescent Display Industry

蛍光表示管材料 : 電卓をこえて広がる用途( 表示材料の進歩)

蛍光表示管材料 : 電卓をこえて広がる用途( 表示材料の進歩)

Life prediction for a vacuum fluorescent display based on two improved models using the three-parameter Weibull right approximation method.

To obtain precise life information for vacuum fluorescent displays (VFDs), luminance degradation data for VFDs were collected from a group of normal life tests. Instead of exponential function, the three-parameter Weibull right approximation method (TPWRAM) was applied to describe the luminance degradation path of optoelectronic products, and two improved models were established. One of these models calculated the average life by fitting average luminance degradation data, and the other model obtained VFD life by combining the approximation method with luminance degradation test data from each individual sample. The results indicated that the test design under normal working stress was appropriate, and the selection of censored test data was simple. The two models improved by TPWRAM both revealed the luminance decaying law for VFD, and the pseudo failure time was accurately extrapolated. It was further confirmed by comparing relative error that using the second model gave a more accurate prediction of VFD life. The improved models in this study can provide technical references for researchers and manufacturers in aspects of life prediction methodology for its development.

Photoluminescence and cathodoluminescence properties of Li<sup>+</sup> doped Gd<sub>1.88</sub>Eu<sub>0.12</sub>O<sub>3</sub>

Li+-doped cubic Gd1.88Eu0.12O3 phosphors were synthesized at 1200 degrees C in air by co-precipitation (CP) and solid state reaction (SS) methods. X-ray diffraction analysis revealed that, regardless of synthetic method, the average crystallite size for Li+-free Gd1.88Eu0.12O3 was approximately 400 nm, then increased with the amount of Li+ and at 20 mol%, reached about 2.3 mu m. Under excitation of the charge transfer band of Eu3+ at 245 nm, Gd1.88Eu0.12O3 exhibited a dominant photoluminescence (PL) red emission peak at 611 nm assigned to the electric dipole transition D-5(0) -> F-7(2) of Eu3+. The red emission peak intensity increased consistently with the amount of Li+-doping, while CP method was found to be effective in improving the red emission intensity at lower amounts of L-i+-doping from 0 to 8 mol%. Cathodoluminescence (CL) property was studied by mounting the synthesized phosphor on a vacuum fluorescent display (VFD) operated at an anode voltage of 50V. The Gd1.88Eu0.12O3 exhibited a similar spectrum with an intense red emission peak at 611 nm, and the highest luminance intensity for the CL red emission was achieved for 8 mol% Li+-doped Gd1.88Eu0.12O3 synthesized by SS method. The evaluation results of PL and CL properties suggested that, besides the crystallite size of Gd1.88Eu0.12O3, dispersion property of Eu3+ ions in the host Gd2O3 was an important factor for improving luminescent properties of Gd1.88Eu0.12O3. Moreover, under the present VFD operating condition at the low excitation voltage, it was thought to be essential for improving CL emission intensity to maintain a sufficient surface area of Gd1.88Eu0.12O3. (C)2015 The Ceramic Society of Japan. All rights reserved.

Synthesis and Luminescence Properties of YNbO4:A (A = Eu3+ and/or Tb3+) Nanocrystalline Phosphors via a Sol–Gel Process

Rare-earth (Eu3+ and/or Tb3+) ions doped YNbO4 phosphors were prepared though a Pechini-type sol–gel process. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy, photoluminescence, and cathodoluminescence spectra were utilized to characterize the synthesized phosphors. XRD reveal that the samples begin to crystallize at 800 °C and pure YNbO4 phase can be obtained at 1000 °C. FE-SEM images indicate that the YNbO4:A (A = Eu3+ and/or Tb3+) samples consist of fine and spherical grains of around 40–80 nm. Under the ultraviolet light (around 255 nm) and low-voltage electron beams, the prepared YNbO4:A (A = Eu3+ and/or Tb3+) phosphors show the characteristic blue broadband emission (from 300 to 500 nm with a maximum around 403 nm) of the YNbO4 host lattice, the characteristic red emission of Eu3+ (5DJ → 7FJ′, J, J′ = 0,1,2,3 transitions) and the characteristic green emission of Tb3+ (5D4 → 7F6,5,4,3 transitions). There exists an energy transfer from the YNbO4 host lattices to Eu3+ (Tb3+) ions. By tuning the relative doping concentration of Eu3+ and Tb3+, a single-composition white-light-emitting has been realized in YNbO4:Eu3+,Tb3+ phosphor. The obtained YNbO4:Eu3+, YNbO4:Tb3+, and YNbO4:Eu3+,Tb3+ phosphors have potential application in the areas of UV white-light-emitting diodes, field emission display devices, and vacuum fluorescent display devices, etc.

P‐96: Development of Fully Integrated Vacuum Fluorescent Display (FIVFD)

VFD (Vacuum Fluorescent Display) is used for various kind of applications such as automotive, audio, video, amusement, household appliance and hot water supply. The futures of VFD are 1 High luminance 2 Wide operating temperature (The response time is less then 10usec.) 3 Wide viewing angle due to self luminance display. Therefore, VFD is installed in the vehicle as audio, meter, clock odo/trip meter, HVAC display. In recent display trend, display content has moved to reconfigurable type form fixed segment type. Especially, multi information display and audio display require reconfigurable type display. On this back ground, high luminance and high resolution reconfigurable VFD was developed. The thin film multilayer wiring technology has allowed high multiplex driving. It was not available at conventional VFD. As a result, 256×64 dots 0.25mm dot pitch reconfiguration, 2000 cd/m2 in luminance display wad developed. Besides, a multi color (Green and Red) VFD was developed also. Now, these displays are on the production.

Reliability Life Prediction of VFD by Constant Temperature Stress Accelerated Life Tests and Maximum Likelihood Estimation

Abstract In order to obtain the life information of vacuum fluorescent display (VFD) in a short time, four constant stress accelerated life tests (CSALT) are conducted with the cathode temperature increased. Lognormal function is applied for describing the life distribution of VFD. Assuming an Arrhenius model, the lognormal parameters are computed by using the maximum likelihood estimation. Furthermore, a self-developed software is employed in predicting the VFD life. The statistical analysis of the results indicates that the test design of CSALT is correct and feasible, that the average life of VFD is over 30,000 h, and that the life-stress relationship satisfies linear Arrhenius equation completely. The precise accelerated parameter is shown to be particularly useful to predict the VFD life within shorter time. Thus, this work provides significant guidelines to help engineers make decisions in design and manufacturing strategy from the aspect of reliability life.

Selective Area Growth of III-Nitride and Their Application for Emitting Devices

In this paper, the high quality AlGaN with high-Al content was grown on in-situ monitoring controlled selective area growth (SAG) GaN and the dislocation density of AlGaN is 1-3×108 cm-2. Furthermore, we use SAG to fabricate InGaN/GaN pyramid structures. CL (Cathodoluminescence) measurements reveal that the thickness, CL peak wavelength and CL intensity gradually increased from the bottom to the top of the facet. Furthermore, Vacuum fluorescent display (VFD) based on InGaN/GaN pyramid structures was demonstrated.

On-Chip ESD Protection Design for Automotive Vacuum-Fluorescent-Display (VFD) Driver IC to Sustain High ESD Stress

A new electrostatic discharge (ESD) protection structure of high-voltage p-type silicon-controlled rectifier (HVPSCR) that is embedded into a high-voltage p-channel MOS (HVPMOS) device is proposed to greatly improve the ESD robustness of the vacuum-fluorescent-display (VFD) driver IC for automotive electronics applications. By only adding the additional n+ diffusion into the drain region of HVPMOS, the transmission-line-pulsing-measured secondary breakdown current of the output driver has been greatly improved to be greater than 6 A in a 0.5- mum high-voltage complementary MOS process. Such ESD-enhanced VFD driver IC, which can sustain human-body-model ESD stress of up to 8 kV, has been in mass production for automotive applications in cars without the latchup problem. Moreover, with device widths of 500, 600, and 800 mum, the machine-model ESD levels of the HVPSCR are as high as 1100,1300, and 1900 V, respectively.

Schematic design of a complex thin-film luminescent screen usable for vacuum fluorescent and field emission display

Based on the facts related to solid-state cathodoluminescence, mixed excitation, and serial excitation recently discovered in our laboratory, a fundamental schematic design and a series of different schematic elaborated designs are proposed for protection from electron accumulation, reasonable use of a luminescent screen, and enhancement of light intensity.

Automatic switching and guidance system to facilitate unassisted uroflowmetry using commercial electronic devices

To enable male patients to undergo uroflowmetry in a private condition without medical supervision, we devised an automatic switching and patient guidance system for the spinning disk uroflowmeter Urodyn 1000, using two commercial electronic devices (an infrared motion sensor tap and a memorizable vacuum fluorescent display). Instead of running the uroflowmeter continuously, which shortens the life of the spinning disk due to mechanical wear, an infrared motion sensor turns on the devices each time a patient enters the room. The patient urinates according to the timely instructions on the visible display and voided urine directly flows into a urinal. The devices are automatically turned off 5 min after the patient leaves the room. With the use of our system, men already acquainted with uroflowmetry could perform self-administered uroflowmetry any time in private. The system was considered useful for improving the quality of patient service.

Constant-step stress accelerated life test of VFD under Weibull distribution case

Constant-step stress accelerated life test of Vacuum Fluorescent Display (VFD) was conducted with increased cathode temperature. Statistical analysis was done by applying Weibull distribution for describing the life, and Least Square Method (LSM) for estimating Weibull parameters. Self-designed special software was used to predict the VFD life. Numerical results showed that the average life of VFD is over 30000 h that the VFD life follows Weibull distribution, and that the life-stress relationship satisfies linear Arrhenius equation completely. Accurate calculation of the key parameter enabled rapid estimation of VFD life.

A Nonlinear Random-Coefficients Model for Degradation Testing

As an alternative to traditional life testing, degradation tests can be effective in assessing product reliability when measurements of degradation leading to failure can be observed. This article presents a degradation model for highly reliable light displays, such as plasma display panels and vacuum fluorescent displays (VFDs). Standard degradation models fail to capture the burn-in characteristics of VFDs, when emitted light actually increases up to a certain point in time before it decreases (or degrades) continuously. Random coefficients are used to model this phenomenon in a nonlinear way, which allows for a nonmonotonic degradation path. In many situations, the relative efficiency of the lifetime estimate is improved over the standard estimators based on transformed linear models.

Data logger for wind resource assessment

Second Wind has released further information on its NOMAD 2 data logger that offers advanced functionality and simplified installation while reducing system costs. Using advanced low-power circuitry, real-time operating system, and Windows◐-compatible Compact Flash Cards, NOMAD 2 collects and secures wind resource data. A vacuum fluorescent display (VFD) option gives a clear bright readout in temperatures down to-40°C and in full sunshine. The LED “heartbeat” provides assurance of normal operation independent of the display. The integrated shelter box design uses innovative mini-rack mounting for power and communications components, so installations are easy to maintain. Field-proven lightning protection circuitry is built in, reducing the number of connections to wire. Larger, colour-coded cage-clamp terminals make wiring faster and easier, even with gloves on. A built-in serial port allows the use of the NOMAD Desktop on site or if the user does not have a laptop the front panel and menuing system provides all required information. Internal 12V batteries allow the unit to run longer, even with transducers and remote communications gear. The NOMAD 2 manages transducer power and sensor excitation to get the most out of the batteries used. A solar package can also be added for perpetual operation and a built-in relay provides added control, including sensor heating for icing conditions. It is possible to connect up to 12 anemometers or other frequency or state devices to the NOMAD 2, including rain gauges, energy meters, and relays. Another 8 analog inputs connect directly to wind vanes, thermistors, and transducers measuring air pressure, electric power, sound level, or anything else that concerns the user at their wind site. This is a short news story only. Visit www.re-focus.net for the latest renewable energy news.

Nitride Phosphors for Low Voltage Cathodoluminescence Devices

ABSTRACTUndoped and Zn doped InGaN microcrystals were synthesized by a two-step method. The InGaN microcrystals have a wurtzite structure and brownish body color. The InGaN samples prepared at 900°C did not contain a metal In phase. The InGaN:Zn microcrystals showed blue photoluminescence (PL) at 77K different from that of GaN:Zn. Reflectivity and photoluminescence excitation (PLE) measurement showed that the fundamental absorption edge of the InGaN:Zn phosphors is 3.47 eV, which implies that the In content in the InGaN:Zn phosphors is less than 0.2%. GaN:Zn and InGaN:Zn showed a Zn related PLE peak at 3.34 eV. InGaN and InGaN:Zn showed an In related PLE peak at 3.14 eV. When the InGaN:Zn samples were selectively excited at 3.15 eV, an In-related emission band centered at 2.2 eV emerged. The InGaN:Zn phosphors mounted on vacuum fluorescent displays (VFDs) showed room-temperature blue cathodoluminescence (CL) and the CL peak shifted slightly toward the low energy compared to that of the GaN:Zn phosphors because of the superimposed In related band. The InGaN:Zn phosphors had a luminance of 50 cd/m2 and a luminance efficiency of 0.03 lm/W at an anode voltage of 50 V.