Pulsed Laser Deposition of Magnesium Oxide and Barium Ternary Oxides for Plasma Display Protective Layers

Abstract

Antud doktoritöös uuriti plasmaekraanide kaitsekihtide materjale ühe plasmaekraanide olulisima parameetri, süttimispinge, seisukohast. Plasmaekraanid koosnevad tuhandtetest gaaslahendusrakkudest ja ekraanide energiatarve ja maksumus on otseselt seotud rakkudes tekitatava gaaslahenduse süttimispingega - mida madalam süttimispinge, seda madalam energiatarve ja seda vähem maksavad ekraanis sisalduvad elektroonikakomponendid. Sünteesitud materjalide süttimispingete mõõtmiseks sadestati uuritavast materjalist kiled spetsiaalsetele alektroodalustele ja mõõdeti kahest vastakuti asetatud alusest koosneva testraku süttimispinge. Õhukeste kilede sadesamiseks kasutati impulss-lasersadestuse seadet. Töös käsitletud materjalideks olid BaGa2O4, BaY2O4 ning puhas ja dopeeritud MgO. Magneesium oksiidi - mis on ka hetkel plasmaekraanis tööstuslikult kasutatav kaitsekihi materjal - korral uuriti sadestustingimuste mõju kasvanud kilede struktuurile ning kilede struktuuri ja dopeerimise mõju gaaslahendusomadustele. Uuriti ka kahe potentsiaalse kaitsekihi asendusmaterjali, BaGa2O4 ja BaY2O4, kilede struktuuri ja gaaslahendusomadusi. Olulisimad faktorid madala süttimispinge saavutamiseks olid MgO kilede korral nende tihedus ja kristallilisus - mida suurem oli kilede tihedus ja kristallilisus, seda väiksem oli süttimispinge. Lisaks selgus analüüsiandmetest, et ka kilede suur pinnakaredus soodustab madala süttimispinge saavutamist. Doktoritöös sünteesiti ka vesinikuga dopeeritud MgO õhukesed kiled. Analüüs näitas, et vesinikulisand tekitas magnesium oksiidi kristallis defekte, mis on võimelised lõksustama elektrone. Need elektronlõksud mõjutasid kilede gaaslahendusomadusi nii, et dopeeritud kilede süttimispinge oli kuni 55 V (20%) madalam kui vesinikulisandita kilede süttimispinge. Kahe uuritud baariumi kolmikoksiidi, BaY2O4 ja BaGa2O4, korral saadi süttimispingete väärtusteks 210 V (BaY2O4) ja 257 V (BaGa2O4), mis on oluliselt kõrgemad võrreldes MgO kiledel mõõdetud väärtustega (<180 V). Tulemus viitab sellele, et need baariumi ühendid pole sobivad MgO asendusmaterjalid kuna nende kasutamine plasmakuvaris ei soodustaks seadme energiatarbe alanemist.

Plasma displays and liquid crystal displays are currently two main large screen display technologies oriented to home-consumers’ market. Besides other elements that influence the PDP characteristics most, the thin layer (protective layer) of MgO in plasma screen is one key element in PDPs and its properties have large influence on the display’s image quality, its lifetime, cost and power consumption. In this work, the morphological and defect structure of MgO thin films was modified by varying film synthesizing conditions. The influence of these modifications on films’ characteristics was studied from the standpoint of PDP applications. Some possible replacement materials for MgO were also investigated. The main attention was turned to the materials group of barium ternary oxides. The thin films, investigated in this work, were synthesized by the pulsed laser deposition (PLD) method. The firing voltage (FV) of the deposited samples, which is the direct indicator of the power consumption of the PDP device (low FV means low power consumption), was measured in our experiments. The density and the crystallinity of the MgO films were the main factors influencing the FV values – high density and crystallinity was accompanied by low FV values of the samples. It was also observed that the high surface roughness of the films favored the achieving of low FVs. MgO films with hydrogen impurities were synthesized. Analysis indicated that the hydrogen impurities in MgO crystal created defects capable of catching electrons. These electron traps influenced the electronic properties of the thin films so that they had up to 55 V (27%) lower FVs than the ones without the hydrogen impurities. Two barium ternary oxides, BaY2O4 and BaGa2O4, were considered as a plasma display protective coating material candidates. The FV values of BaY2O4 (210 V) and BaGa2O4 (257 V) were considerably higher as compared to the FVs of MgO films (<180 V), which indicates that these barium oxides are not promising replacement materials to MgO. Because of considerably higher FVs, these materials would not favor lower power consumption of a PDP device.