Results are presented from a systematic investigation to design and optimize a low-pressure chemical vapor deposition (CVD) process for manganese-doped zinc sulfide (ZnS:Mn) thin films for electroluminescent (EL) device applications. The CVD process used diethylzinc (DEZ), di-π-cyclopentadienyl manganese (CPMn), and hydrogen sulfide (H2S) as co-reactants and hydrogen (H2) as carrier gas. A design of experiments approach was used to derive functionality curves for the dependence of ZnS:Mn film properties on substrate temperature and flow rates (partial pressures) of DEZ, CPMn, H2S, and H2. Film physical, chemical, structural, and optical properties were examined using Rutherford backscattering spectrometry, dynamic secondary ion mass spectroscopy, x-ray photoelectron spectroscopy, nuclear-reaction analysis, x-ray diffraction, transmission electron microscopy, atomic force microscopy, and scanning electron microscopy. EL measurements were carried out on ZnS:Mn-based dielectric–sulfur–dielectric stacks incorporated into alternating-current thin-film electroluminescent devices. An optimized process window was established for the formation of films with predominantly (0 0 2) orientation, grain size larger than 0.2 μm, and Mn dopant level approximately 0.5 at.%. A brightness of 407 cd/m2 (119 fL) and efficiency of 1.6 lm/W were obtained, as measured at 40 V above threshold voltage and 60 Hz frequency.

A systematic 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 dissociation 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, 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. (C) 2001 The Electrochemical Society.

Abstract— Active‐matrix electroluminescent (AMEL) microdisplays have been known for their numerous beneficial characteristics such as low weight, compactness, high brightness, and high contrast ratio. Beside these desirable characteristics, some of their drawbacks include difficulty in obtaining a high number of gray‐scale levels or a large number of colors, and interface‐electronics complexity. To address these drawbacks, AMEL displays using an analog addressing architecture have been developed. Utilizing this new driving scheme, 256 monochrome levels or 16 million colors are obtainable. Gray shade is proportional to an analog voltage stored on the hold node of each pixel. For color displays, each pixel is comprised of red, green, and blue subpixels arranged in vertical stripes, and can be sized independently to achieve the appropriate white balance. With the integration of control‐signal circuit blocks on the same substrate as the microdisplay, the number of input control signals is minimized and the display can be driven with very simple interface electronics. This results in low overall system cost, compact electronic packaging, and low power consumption. To accommodate most optical orientations, the display has built‐in modes to flip the image both vertically and horizontally. Additionally, the display supports multiple interlace addressing modes.

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 degrees 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 (H2S) as reactants. Various Sr and H2S reactant flows and associated partial pressures were examined to explore corresponding effects on the him's 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 mu m, and Ce dopant level similar to 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. (C) 2000 The Electrochemical Society. S0013-4651(99)06-079-6. All rights reserved.

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), 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), 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), 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.

Abstract— Active‐matrix‐electroluminescent (AMEL) displays using ZnS phosphors have demonstrated sufficient luminance, contrast, and stability under high‐frequency drive for commercial applications. Recently, color AMEL displays have been fabricated using either spatial or temporal filtering of the SrS: Ce/ZnS: Mn broad‐band emission. The SrS: Ce/ZnS: Mn broad‐band phosphor shows improved spectral balance under AMEL drive conditions. Higher‐efficiency blue emission remains the primary goal for achieving lower power in both active‐ and passive‐matrix color EL displays.

A full color thin film electroluminescent (TFEL) display can be fabricated by using color filters in combination with a high efficiency ‘white’ phosphor, such as a thin film multilayered stack of ZnS:Mn and SrS:Ce (denoted ZnS:Mn/SrS:Ce). To date, deposition of these multilayers has been limited to vacuum evaporation techniques and atomic layer epitaxy, both of which require different substrate temperatures for growth of high quality ZnS:Mn and SrS:Ce. This repeated thermal cycling during multilayer deposition can adversely affect electroluminescent (EL) performance and manufacturability. Sputter deposition of ZnS:Mn and SrS:Ce produces high quality phosphors for a wider range of substrate temperatures. We have determined a common set of radio frequency (rf) sputter deposition parameters for ZnS:Mn and SrS:Ce that result in high performance, multilayered white phosphors for use in TFEL devices. The EL performance of our samples is comparable to the best performance reported for evaporated multilayered samples. The major improvement is that the rf sputtered ZnS:Mn and SrS:Ce layers were deposited at the same substrate temperature. We report on the effects of sputter deposition parameters on the resultant composition and morphology of ZnS:Mn and SrS:Ce thin films and multilayers. Their EL performance was evaluated and correlated to composition and morphology.

This project helped to develop a metal-organic chemical vapor deposition (MOCVD) method that could improve the efficiency of the blue phosphor for full color thin-film electroluminescent (TFEL) flat panel displays. High quality SrS and SrS:Ce thin films were deposited from Sr(thd)2, Ce(thd)4 and H2S via a low pressure MOCVD process. Film characteristics were found to be insensitive to the presence of the cerium dopant in the concn. range investigated. Depositions were carried out for a wide temp. range (250-550°C). Deposition rates were found to be relatively insensitive for the temp. range investigated. The films produced were found to be highly cryst. at all temps. investigated. Deposited material showed texturing as a function of substrate material and temp. FWHM of the a 111 ii reflections were found to have a 2Q values of 0.15-0.18 deg. for all temps. RBS and AES shows stoichiometric 1 : 1 SrS with less than 2% carbon and oxygen contaminates. ERO indicates the films to have 1- 2.5% hydrogen. Films doped with 0.019-0.043 atom % Ce showed weak blue-green to green PL with increasing dopant concn. Doped films yielded up to 3.2 cd/m2 EL emission with CIE coordinates of x = 0.22 and y = 0.32 and turn-on voltages of 150-250 V.