Christopher N. King

A Polysilicon Active Matrix Organic Light Emitting Diode Display with Integrated Drivers

The design of an active matrix organic light emitting diode (AMOLED) display using a polysilicon thin film transistor pixel is described. Characteristics of the OLED response in the low current regime are described and their impact on the design of integrated driver circuitry is discussed. Integrated data and select scanners which generate the signals necessary for data capture and pixel calibration are presented.

Capacitance‐voltage characteristics of alternating‐current thin‐film electroluminescent devices

The capacitance‐voltage (C‐V) technique is proposed as a method for characterization of the electrical properties of alternating‐current thin‐film electroluminescent (ACTFEL) display devices. Analysis of the C‐V and aging characteristics of ZnS:Mn ACTFEL devices indicates that the C‐V technique is complementary to the charge‐voltage technique in the extraction of device physics information.

In Situ Pulsed Deposition Studies of Ce ( tmhd ) 4 on SrS Surfaces for Thin Film Electroluminescent Flat Panel Display Applications

In this paper, results are presented from a systematic investigation which aimed to evaluate the performance and efficiency of tetrakis(2,2,6,6-tetramethyl-3,5-heptadionato)cerium(IV), or Ce(tmhd) 4 , as the cerium dopant source in the atomic layer epitaxy (ALE) of strontium sulfide (SrS) thin films for thin film electroluminescent (TFEL) display applications. For this purpose, in situ growth and characterization studies of the adsorption and associated nucleation mechanisms of Ce(tmhd) 4 on SrS surfaces were performed in a clustered system under tightly controlled ultraclean conditions. The growth experiments were carried out in a specially designed processing chamber under pulsed deposition conditions that emulated the ALE process. The samples were then transferred in situ, without exposure to air, to various characterization chambers where compositional and chemical analyses were readily performed. In particular, chemical evaluation by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy showed incomplete decomposition of the Ce(tmhd) 4 molecule with the observation of high carbon levels corresponding to ligands from the precursor. It is believed that these ligands sterically hinder subsequent adsorption and nucleation of the Sr source by poisoning the substrate surface, and therefore require repeated cycles of exposure to pulses of the Sr source and associated reactants to ensure their complete removal. It is thus suggested that the incomplete decomposition of the Ce(tmhd) 4 molecule is the primary cause for its poor efficiency as Ce source precursor, an observation supported by experimental findings from actual ALE manufacturing of SrS:Ce films for TFEL applications.

Electrical characterization of blue electroluminescent devices

A new class of blue thin-film electroluminescent (TFEL) devices based on thiogallate phosphors has been reported recently. The purpose of this work reported herein is to compare and contrast the electrical properties of CaGa2S4:Ce TFEL blue phosphor devices to those of conventional evaporated ZnS:Mn TFEL devices. Capacitance-voltage (C-V) and internal charge-phosphor field (Q-Fp) techniques are employed for electrical characterization.

In Situ Studies of the Nucleation Mechanisms of Tris(cyclopentadienyl)Cerium as Cerium Dopant Source in SrS:Ce Thin Films for Electroluminescent Displays

A systematie evaluation was made of the performance and efficiency of tris (cyclopentadienyl)cerium, Ce(CPD), as potential dopant source in atomic layer epitaxy (ALE) and chemical vapor deposition (CVD) of Ce-doped strontium sulfide (SrS:Ce) for thin-film electroluminescent display applications. In situ growth and characterization studies were carried out, without a vacuum break, of the adsorption and associated dissocation mechanisms of Ce(CPD) within the substrate temperature window typically employed in ALE and CVD SrS:Ce. Associated findings were compared to results from tetrakis (2,2,6,6-tetramethyl-3,5 heptadionato)cerium, Ce(tmhd) 4 , which was used as a comparative performance baseline. In this respect. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry studies indicated that, within the typical thermal budget used in ALE and CVD of SrS:Ce films, the Ce(CPD) source decomposed more efficiently than its Ce(tmhd) 4 counterpart, as supported by the observation of reduced hydrocarbon-based surface contamination and a cleaner Ce phase. It was concluded that Ce(CPD) might be a better candidate than Ce(tmhd) 4 for applications as Ce dopant source in ALE and CVD SrS:Ce films.

Metallorganic Chemical Vapor Deposition of SrS:Ce for Thin Film Electroluminescent Device Applications

Results are presented from a systematic study to develop and optimize a metallorganic chemical vapor deposition process for the growth of high brightness cerium-doped strontium sulfide (SrS:Ce) thin films for electroluminescent (EL) display applications. Growth of SrS:Ce was investigated in the temperature range from 400 to 530°C using strontium(2,2,6,6-tetramethyl-3,5-heptadionato)trimer (Sr(tmhd) 2 trimer), tetrakis(2,2,6,6-tetramethyl-3,5-heptadionato)cerium (Ce(tmhd) 4 ), and hydrogen sulfide (H 2 S) as reactants. Various Sr and HAS reactant flows and associated partial pressures were examined to explore corresponding effects on the films physical, chemical, and optical properties. Film structural and compositional properties were analyzed by Rutherford backscattering spectrometry, nuclear reaction analysis for hydrogen profiling, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy, EL measurements were carried out on SrS:Ce-based dielectric-sulfur-dielectric stacks. The results of these studies yielded key correlations between process parameters and film texture, grain size, and EL performance In particular, the highest EL performance was obtained for films with a predominantly (200) orientation, grain size larger than 1.0 μm, and Ce dopant level ∼0.14 atom %. A brightness of 51 cd/m 2 and efficiency of 0.22 lm/W were observed, as measured at 40 V above threshold voltage and 60 Hz frequency.

MOCVD OF SrS and SrS:Ce Thin Films for Eelctroluminescent Flat Panel displays

High quality SrS and SrS:Ce thin films were deposited from Sr(thd) 2 , Ce(thd) 4 and H 2 S via a low pressure MOCVD process. Film characteristics were found to be insensitive to the presence of the cerium dopant in the concentration range investigated. Depositions were carried out for a wide temperature range (250–550° C). Deposition rates were found to be relatively insensitive for the temperature range investigated. The films produced were found to be highly crystalline at all temperatures investigated. Deposited material showed texturing as a function of substrate material and temperature. FWHM of the reflections were found to have a 2Θ values of 0.15–0.18 deg. for all temperatures. RBS and AES shows stoichiometric 1:1 SrS with less than 2% carbon and oxygen contaminates. ERD indicates the films to have 1 – 2.5% hydrogen. Films doped with 0.019 – 0.043 atom – 250 volts.

High-luminance active matrix electroluminescent (AMEL) display for see-through symbology applications

An Active Matrix Electroluminescent (AMEL) miniature display is reported with over 1000fL luminance. This technology is demonstrated on a 0.7-inch diagonal 640 X 480 display. This achievement was made possible primarily through improvements in the AMEL design and process technology. Additionally, by addressing the display with only one bit of grayscale data, more of the frame time is available for applying light generating voltage pulses to the phosphor. This paper discusses the key characteristics of this display, including luminance, contrast, and power consumption. Details of luminance and grayscale tradeoffs are explained. System drive electronics used to interface this display to common video sources are also described.

0.7-in. 1280x1024 active-matrix electroluminescent display using a 12-μm pixel structure

Using a 12 by 12 micrometers pixel cell and 1.0 micrometers deign rules, a 0.7-inch diagonal 1280 by 1024 active matrix electroluminescent (AMEL) display has been designed and demonstrated using a silicon-on-insulator based CMOS technology. The display accepts data at 100 MHz via eight data inputs and provides five bits of gray scale. A total of 24 connections are used for all display functions. Architecture, theory of operation, and detailed specification for this new 2000 line-per-inch display will be discussed. The display is the same size as Planars previously developed AMEL 640 by 480 arrays, thus providing over tour times the number of pixels in the same footprints as the prior design. The display provides workstation resolution in an extremely compact format and offers the same environmental robustness and optical performance as previously demonstrated in 1000 line-per-inch AMEL displays.

Blue And Yellow Light Emitting Phosphors For Thin Film Electroluminescent Displays

Following a description of the purpose and participating members in the Phosphor Technology Center of Excellence, research on the growth and characterization of modulation doped ZnS:Mn and of Ca 0.95 Sr 0.05 Ga 2 S 4 :6%Ce are reported. ZnS:Mn has been grown using MOCVD and incorporation of Mn in 1 to 5 layers from 5 to 20 nm thick separated by layers of pure ZnS from 5 to 50 nm thick. This is shown to result in lower threshold voltages for ACTFELD displays. The luminescence spectra from sputter deposited, cerium-doped thiogallate thin films were measured and the diffusion of thin ZnS passivation layers versus temperature of heat treatment was discussed.