Thin film of Lead Titanate was deposited onto both the titanium and Corning 7059 glass substrates by Chemical Vapor Deposition (CVD) process involving the application of vapor mixtures of Pb, $Ti(C_2H_5O)_4$, and oxygen.
Analyses of Auger Electron Spectroscopy(AES) and X-ray Photoelectron Spectroscopy(XPS) have been performed in order to find a chemical composition of Lead Titanate films. Impurities were not found in the film after sputter cleaning. AES analysis has shown that the interlayer ($TiO_2$ and $TiO$) formed between the $PbTiO_3$ layer and titanium substrate.
The effects of the deposition temperature, the gas flow rate, and the composition of reactant gases on the deposition rate, preferred orientation, and the surface morphology of the Lead Titanate deposit have been also studied.
The experimental results indicated that the CVD of Lead Titanate was a thermally activated process with an apparent activation energy of 21.8 kcal/mol and the Chemical Vapour Deposition of Lead Titanate was governed by the surface chemical reaction at the deposition temperature between 450℃ and 800℃ and with the reactant gas flow rate above 750 sccm. Below 750 sccm, deposition reaction was controlled by the external mass transfer and surface chemical reaction. Furthermore, the critical gas flow rate at which the deposition mechanism switches from external mass transfer and surface chemical reaction to the surface chemical reaction increases with increasing deposition temperature.
The deposition rate, the crystal size, and the crystal growth along the (001) preferred orientation were increased with an increase in the deposition temperature.
It was found by Auger Electron Spectroscopy (AES) that the film stoichiometry was obtained at the Lead Titanate deposited at the deposition temperature, 750℃; the $Ti(C_2H_5O)_4$ fraction, 0.15; and $O_2$ partial pressure, 0.06 atm. The comparison of AES and XPS analysis shows nearly similar results for chemical composition of the Lead Titanate.
The measured dielectric constant of the ferroelectric Lead Titanate was about 120. The dielectric constant has a characteristic bend at a thickness of 1.5 ㎛.
The Lead Titanate having a stoichiometric composition has a curie point of 480℃ and a dc conductivity of $3.2 × 10^{-12} Ω^{-1}.cm^{-1}$ at room temperature. Both a well-defined dielectric anomaly and a break in dc conductivity were observed at the phase transition temperature 480℃ for film of the thickness of 4.7 ㎛.
To find a ferroelectric property, hysteresis loop has been measured. The nonsaturating loops in the films deposited at 650℃ and 700℃ may be attributed to a complex conduction process due to the contaminants ($TiO_2$ and $TiO$). The ferroelectric properties of the $PbTiO_3$ film having a stoichiometric composition were remanent polarization, 14.1μC/㎠; coercive field, 20.16kV/cm.
The optical transmittance of the Lead Titanate film was about 50% at 5㎛ thickness. It might be affected by the microstructure of film.
IV-3.
화학증착법을 이용하여 강유전체 재료인 Lead Titanate 박막을 제조하였다.
IV-3-1. Substrate reaction
Pbo와 모재인 티타늄과의 반응에서 Lead Titanate를 제조하여 다음 결과를 얻었다.
1. $PbTiO_3$ 증착층은 주상정 조직을 가지며 모재에 수직으로 성장한다.
2. $PbTiO_3$ 박막과 모재사이에 titanium dioxide의 interlayer가 형성되었다.
3. $PbTiO_3$의 유전상수와 유전손실은 박막두께에 관계없이 일정하며 양호한 성질을 나타낸다.
VI-3.
$Pb, Ti(C_2H_5O)_4, O_2$의 혼합 기체를 이용한 Lead Titanate의 화학 화학증착에서 증착층의 화학 조성을 AES 와 XPS 를 사용하여 얻어서 다음과 결론을 얻었다.
(1) 표준 시편을 사용하여 $PbTiO_3$ 증착층의 조성을 AES 와 XPS로 분석하였다.
Table.14 Comparison XPS and AES results for a sputter cleaned $PbTiO_3 sample. XPS was performed at the take-off angles $\varphi=45˚$ to the normal to the sample.
◁표 삽입▷ (원문을 참조하세요)
Deposition condition: deposition temperature, 750℃; Ti(C_2H_5O)_4$ fraction, 0.15; $O_2$ partial pressure, 0.06 atm; total gas flow rate, 800 sccm
Table.15 Atomic compositions of the $PbTiO_3$ films for various deposition temperatures (by XPS)
◁표 삽입▷ (원문을 참조하세요)
Table.16 Atomic compositions of the $PbTiO_3$ films for various $Ti(C_2H_5O)_4$ fractions(by XPS)
◁표 삽입▷ (원문을 참조하세요)
(2) 반응기체유량 800sccm, $Ti(C_2H_5O)_4$ 분율0.15, $O_2$분압 0.06atm, 증착온도가 600, 650, 700℃범위에서 화학증착한 $PbTiO_3$의 증착층은 nonstoichiometry를 이루며, 750℃에서 증착한 증착층은 stoichiometry를 이룬다.
(3)(2)번과 같은 증착조건에서 $Ti(C_2H_5O)_4$ 분율이 0.08일 경우에 stoichiometry를 이루며, 그 이상에서는 nonstoichiometry를 이룬다.
(4) XPS분석에 의한 Lead Titanate의 조성은 반응변수에 관계없이 거의 일정하며 AES분석과 비교할때 거의 비슷한 결과를 보인다.
