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Dependence of structural and luminescent characteristics of Y2O3:Er thin film phosphors on substrate
Applied Surface Science 212–213 (2003) 815–819
Dependence of structural and luminescent characteristics of Y2O3:Er thin film phosphors on substrate Yoichiro Nakanishia,b,*, Kenji Kimuraa, Hiroko Kominamib, Hiroyoshi Nakajimab, Yoshinori Hatanakac, Goro Shimaokaa b
a Research Institute of Electronics, Shizuoka University, 3-5-1 Johoku, Hamamatsu 432-8011, Japan Graduate School of Electronic Science and Technology, Shizuoka Universisty, 3-5-1 Johoku, Hamamatsu 432-8011, Japan c Faculty of Engineering, Aichi University of Technology, 50-2 Nishisako-cho, Gamagori 443-0047, Japan
Abstract The dependence of the structural and cathodoluminescent (CL) characteristics of green-emitting Y2O3:Er thin films phosphors deposited by electron beam evaporation on substrate used for the Y2O3:Er thin film deposition has been investigated. Quartz glass, ITO glass and c-axis-oriented ZnO thin film substrates were used as the substrate. Best crystallinity and CL luminance were obtained from the Y2O3:Er thin film deposited on the ZnO thin film substrate. One of the reason for this fact might be due to high conductivity the substrate. The other might be due to better crystallinity of Y2O3:Er thin film deposited on the ZnO thin film substrate than that on the quartz and ITO substrates, because of the best crystallinity of the ZnO thin film substrate among three substrates. The Y2O3:Er thin film deposited at 500 8C on the ZnO thin film and annealed at 800 8C for 1 h in O2 flow showed CL luminance of 70 cd/m2 with pure green emission under excitation by electron beam with 3 kV, 60 mA/cm2. # 2003 Elsevier Science B.V. All rights reserved. PACS: 78.60.Hk, cathodoluminescence, ionoluminescence; 78.55.m, photoluminescence; 85.45.Fd, field emission displays (FEDs); 68.55.a, thin film structure and morphology Keywords: Y2O3; Er; Phosphor; Thin film; Electron beam evaporation; Cathodoluminescence
1. Introduction Field emission display (FED) is one of the most promising displays as full color flat panel display, because of several advantages such as high picture quality, wide view angle, wide temperature range for driving, high response speed, and low power consumption [1]. Development of new electron sources for the field emission such as carbon nano tubes [2], *
Corresponding author. Tel.: þ81-53-478-1346; fax: þ81-53-478-1346. E-mail address: [email protected] (Y. Nakanishi).
ballistic electron surface-emitting devices (BSD) [3], metal–insulator–metal (MIM) cathode [4] in addition to Spindt type cathode promotes the development of FEDs. On the other hand, FED operates at lower anode voltages and high current densities. One serious impediment to the success of FED is lack of stable phosphors with high efficiency under high electron density excitation. CRT phosphor, which show high efficiency, degrade at high current density excitation and as a result, the luminescence yield decreases with formation of a dead layer on the phosphor surface [5]. Moreover, the degradation leads to contamination of the cathode components and decreases the lifetime of
0169-4332/03/$ – see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0169-4332(03)00065-5
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Y. Nakanishi et al. / Applied Surface Science 212–213 (2003) 815–819
FED [6]. Therefore, development of phosphors with high luminance and efficiency for FEDs is one of key technologies to realize high performance FEDs. Recently, there has been significant research interest in the development of Y2O3:Eu thin film phosphor for FED applications [7–9] because of its host with simple structure and stability and efficient luminescence. The advantage of the thinner phosphor screens are improved conduction, light transmission, special resolution, reduced saturation effects, better thermal stability, etc. [10]. In this paper, Er-activated Y2O3 as a green-emitting thin film phosphor was investigated by considering the stability of the Y2O3 lattice and the green emission from Er3þ ion independent on its concentration and host matrix [11].
2. Experimental Y2O3:Er thin films were deposited by an electron beam evaporation. In this experiment, three kinds of substrates were used at the same time deposition to evaluate the dependence of the structural and cathodoluminescent (CL) properties on substrate. The first is a quartz glass substrate, the second is ITO film deposited glass substrate, where ITO is amorphous like, the third is c-axis-oriented ZnO thin film substrate. A pellet as evaporation source was made by pressing and the heating mixture of Y2O3 (99.99%) and 2 mol% Er2O3 (99.9%) at 1000 8C for 3 h in air. The evaporation was carried out at a vacuum pressure of the order of 105 Torr. The thickness of the films was controlled to make about 500 nm using crystal thickness monitor. The films were deposited at substrate temperatures of 400 and 500 8C. The film deposited at 400 8C showed [1 0 0] orientation, whereas the film at 500 8C showed [1 1 1] orientation. As the crystallinity and CL luminance of the film at 400 8C were very poor, the experimental results of the films deposited at 500 8C are described in this paper. The ZnO thin film used as the substrate for Y2O3:Er thin film was deposited on a quartz glass by rf magnetron sputtering using ZnO target, where substrate temperature, total pressure and electric power were room temperature, 1 102 Torr and 200 W, and atmosphere was the mixture of 20% Ar and 80% O2. The ZnO film was annealed at 800 8C for 1 h in
Fig. 1. XRD curves of as-deposited and annealed ZnO thin films used as substrate for the deposition of Y2O3:Er thin film.
Ar to improve the crystallinity. Fig. 1 shows XRD curves of as-deposited and annealed films. It can be seen that the ZnO show c-axis orientation and the crystallinity is improved considerably by the annealing. All the as-deposited and annealed Y2O3:Er films were characterized by X-ray diffraction (XRD) and chathodoluminescence measurement. A continuous electron beam with a spot size of about 2 106 m2 was used to excite the Y2O3:Er phosphor films. The CL luminance and color coordinates were measured at room temperature using a luminance meter (TOPCON, BM-5A).
3. Results and discussion 3.1. On quarts glass substrates The Y2O3:Er thin films were annealed in air for 1 h at 600, 700 and 800 8C after the deposition at 500 8C on each substrate. Fig. 2 shows dependence of (a) XRD curves and (b) luminance versus anode voltage (L–V) characteristics of Y2O3:Er films deposited on quartz glass substrates on annealing temperature. It can be seen from (a) that the crystallinity of the film is improved with increasing annealing temperature. The result (b) shows that about 13 cd/m2 is obtained from the film annealed at 800 8C under excitation with 3 kV, 60 mA/cm2, and the annealing temperature dependence is small. The reason for the latter result is thought that as the quartz substrate is insulator, the film surface takes charging-up under excitation with electron beam, so the annealing effect is not reflected.
Y. Nakanishi et al. / Applied Surface Science 212–213 (2003) 815–819
Fig. 2. Dependence of (a) XRD curves and (b) L–V characteristics of Y2O3:Er thin films deposited on quartz glass substrates on annealing temperature.
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Fig. 3. Dependence of (a) XRD curves and (b) L–V characteristics of Y2O3:Er thin films deposited on ITO glass substrates on annealing temperature.
3.2. On ITO glass substrates
3.3. On c-axis-oriented ZnO thin film substrates
Fig. 3 shows dependence of (a) XRD curves and (b) L–V characteristics of the films on ITO substrates on annealing temperature. It should be noticed from (a) that the crystallinity of the films deteriorates by the annealing at higher than 700 8C. We have reported that mutual diffusion at the interface of Y2O3 and ITO is caused by the annealing even at 500 8C [12]. Therefore, the poor crystallinity of the film annealed at 700 and 800 8C shown in Fig. 3(a) seems to be due to the mutual diffusion between Y2O3 and ITO. Whereas the luminance increases with increasing annealing temperature. The reason for this fact is thought that ITO is conductive, so the charging-up on the surface is suppressed, moreover, the formation of a Er luminescence center, such as substitution of Er to Y site, is promoted by annealing at higher temperature. However, the luminance at 3 kV, 60 mA/cm2 is about 12 cd/m2 which is same as the case of the quartz substrate. This poor luminance seems to be due to the poor crystallinity.
Fig. 4 shows dependence of (a) XRD curves and (b) L–V characteristics of the films deposited on c-axisoriented ZnO thin films substrate. It should be emphasized from (a) that the film with higher crystallinity than that of the film with highest crystallinity on the quartz substrate is obtained even from as-deposited film. This fact suggest that the crystallinity of the film depends considerably on crystalline state of the substrate even if substrate is polycrystalline and amorphous. The best FWHM of 0.198 is obtained at 700 8C annealing, although nearly the same FWHM is obtained from the films as-deposited and annealed at other temperatures. It should be noticed from Fig. 4(b) that the luminance of the films is much higher than that of the films on the quartz and ITO substrates. The highest luminance of about 70 cd/m2 is obtained at 3 kV, 60 mA/cm2 excitation. These results suggest that the thin film phosphors can be used for the phosphor screen for FEDs using c-axis-oriented ZnO
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Y. Nakanishi et al. / Applied Surface Science 212–213 (2003) 815–819
Fig. 5. CL spectra of Y2O3:Er thin films deposited on the ZnO thin film substrates and annealed at several temperatures.
Fig. 4. Dependence of (a) XRD curves and (b) L–V characteristics of Y2O3:Er thin films deposited on c-axis-oriented ZnO thin films substrate on annealing temperature.
the penetration depth of the electron beam with the energy of 3 kV is smaller than 100 nm, whereas the thickness of Y2O3:Er film is about 500 nm. Therefore, it can be concluded that the CL emission obtain in this experiment is from Y2O3:Er thin films. Moreover, independence of the spectra on the annealing and substrate is based on the nature of f–f transition in trivalent rare-earth ion. The CIE coordinates of the emission are (0.32, 0.62), which is very pure green for full color display.
4. Summary film as transparent electrode in FEDs, although the luminance should be improved for practical use. In the case of ZnO film substrate, the luminance of the film annealed at 700 8C is a little higher than that of the film annealed at other temperature. The cause of this fact is not understood at present. 3.4. CL spectra Fig. 5 shows CL spectra of the Y2O3:Er thin films deposited on the ZnO film substrates under excitation with 3 kV and 60 mA/cm2. The spectra shown in the figure is the emission from f–f transition in Er ion, where main peak is by 4 S3=2 ! 4 I15=2 transition [11]. On the other hand, it is well-known that Zn-rich ZnO (ZnO:Zn) phosphor and thin film phosphor show a broad emission with a peak at around 510 nm [13]. However, the emission from the ZnO:Zn cannot be observed in the spectra shown in Fig. 5. It is because
The effect of the substrate for the structural and CL properties of Er-doped Y2O3 thin film phosphors has been investigated. The quartz, ITO and c-axis-oriented ZnO thin film were used as the substrate. The ZnO film substrate was most effective for both the structural and CL properties. It is concluded that this result is due to the good crystallinity and high conductivity of the ZnO thin film. The Y2O3:Er film on ZnO film annealed at 700 8C showed a CL luminance of about 70 cd/m2 and CIE coordinates of (0.32, 0.62). The green emission from this film is very good chromaticity, although the CL luminance should be improved.
References [1] S. Itoh, T. Watanabe, T. Yamaura, K. Yanao, in: Technical Digest of Asia Display’95, Hamamatsu, Japan, 1995, p. 617.
Y. Nakanishi et al. / Applied Surface Science 212–213 (2003) 815–819 [2] Y. Saito, S. Uemura, K. Hamaguchi, Jpn. J. Appl. Phys. 37 (1998) L346. [3] T. Komoda, Y. Honda, T. Hatai, Y. Watabe, T. Ichihara, K. Aizawa, Y. Kondo, X. Sheng, A. Kojima, N. Koshida, in: Proceedings of SID’00, Long Beach, CA, 2000, p. 428. [4] T. Kusunoki, M. Suzuki, IEEE Trans. Electron. Devices 47 (2000) 1667. [5] D.J. Robins, J. Electrochem. Soc. 127 (1980) 2694. [6] S. Itoh, T. Kimizuka, T. Tenegawa, J. Electrochem. Soc. 136 (1989) 1819. [7] J. McKittrick, G.A. Hirata, C.F. Bacalski, R. Sze, J. Mourant, K.M. Hubbard, S. Pattilo, K.V. Salazar, M. Trkula, T.R. Gosnell, J. Mater. Res. 13 (1988) 3019.
819
[8] K.G. Cho, D. Kumar, S.L. Jones, D.G. Lee, P.H. Holloway, R.K. Singh, J. Electrochem. Soc. 145 (1998) 3456. [9] Y. Nakanisi, H. Wada, H. Kominami, M. Kottaisamy, T. Aoki, Y. Hatanaka, J. Electrochem. Soc. 146 (1999) 4320. [10] G.A. Hirata, J. McKittrick, M. Avalos-Borja, J.M. Siqueiros, D. Derlin, Appl. Surf. Sci. 113–114 (1997) 509. [11] E.W. Chase, R.T. Hepplewhite, D.C. Krupka, D. Kahng, J. Appl. Phys. 40 (1969) 2512 (in Japanese). [12] Y. Nakanisi, Y. Suzuki, G. Zhou, M. Ogita, Y. Fukuda, G. Shimaoka, J. Surf. Sci. Soc. Jpn. 10 (1989) 399. [13] Y. Nakanishi, A. Miyake, H. Kominami, T. Aoki, Y. Hatanaka, G. Shimaoka, Appl. Surf. Sci. 142 (1999) 233.
Dependence of structural and luminescent characteristics of Y2O3:Er thin film phosphors on substrate Yoichiro Nakanishia,b,*, Kenji Kimuraa, Hiroko Kominamib, Hiroyoshi Nakajimab, Yoshinori Hatanakac, Goro Shimaokaa b
a Research Institute of Electronics, Shizuoka University, 3-5-1 Johoku, Hamamatsu 432-8011, Japan Graduate School of Electronic Science and Technology, Shizuoka Universisty, 3-5-1 Johoku, Hamamatsu 432-8011, Japan c Faculty of Engineering, Aichi University of Technology, 50-2 Nishisako-cho, Gamagori 443-0047, Japan
Abstract The dependence of the structural and cathodoluminescent (CL) characteristics of green-emitting Y2O3:Er thin films phosphors deposited by electron beam evaporation on substrate used for the Y2O3:Er thin film deposition has been investigated. Quartz glass, ITO glass and c-axis-oriented ZnO thin film substrates were used as the substrate. Best crystallinity and CL luminance were obtained from the Y2O3:Er thin film deposited on the ZnO thin film substrate. One of the reason for this fact might be due to high conductivity the substrate. The other might be due to better crystallinity of Y2O3:Er thin film deposited on the ZnO thin film substrate than that on the quartz and ITO substrates, because of the best crystallinity of the ZnO thin film substrate among three substrates. The Y2O3:Er thin film deposited at 500 8C on the ZnO thin film and annealed at 800 8C for 1 h in O2 flow showed CL luminance of 70 cd/m2 with pure green emission under excitation by electron beam with 3 kV, 60 mA/cm2. # 2003 Elsevier Science B.V. All rights reserved. PACS: 78.60.Hk, cathodoluminescence, ionoluminescence; 78.55.m, photoluminescence; 85.45.Fd, field emission displays (FEDs); 68.55.a, thin film structure and morphology Keywords: Y2O3; Er; Phosphor; Thin film; Electron beam evaporation; Cathodoluminescence
1. Introduction Field emission display (FED) is one of the most promising displays as full color flat panel display, because of several advantages such as high picture quality, wide view angle, wide temperature range for driving, high response speed, and low power consumption [1]. Development of new electron sources for the field emission such as carbon nano tubes [2], *
Corresponding author. Tel.: þ81-53-478-1346; fax: þ81-53-478-1346. E-mail address: [email protected] (Y. Nakanishi).
ballistic electron surface-emitting devices (BSD) [3], metal–insulator–metal (MIM) cathode [4] in addition to Spindt type cathode promotes the development of FEDs. On the other hand, FED operates at lower anode voltages and high current densities. One serious impediment to the success of FED is lack of stable phosphors with high efficiency under high electron density excitation. CRT phosphor, which show high efficiency, degrade at high current density excitation and as a result, the luminescence yield decreases with formation of a dead layer on the phosphor surface [5]. Moreover, the degradation leads to contamination of the cathode components and decreases the lifetime of
0169-4332/03/$ – see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0169-4332(03)00065-5
816
Y. Nakanishi et al. / Applied Surface Science 212–213 (2003) 815–819
FED [6]. Therefore, development of phosphors with high luminance and efficiency for FEDs is one of key technologies to realize high performance FEDs. Recently, there has been significant research interest in the development of Y2O3:Eu thin film phosphor for FED applications [7–9] because of its host with simple structure and stability and efficient luminescence. The advantage of the thinner phosphor screens are improved conduction, light transmission, special resolution, reduced saturation effects, better thermal stability, etc. [10]. In this paper, Er-activated Y2O3 as a green-emitting thin film phosphor was investigated by considering the stability of the Y2O3 lattice and the green emission from Er3þ ion independent on its concentration and host matrix [11].
2. Experimental Y2O3:Er thin films were deposited by an electron beam evaporation. In this experiment, three kinds of substrates were used at the same time deposition to evaluate the dependence of the structural and cathodoluminescent (CL) properties on substrate. The first is a quartz glass substrate, the second is ITO film deposited glass substrate, where ITO is amorphous like, the third is c-axis-oriented ZnO thin film substrate. A pellet as evaporation source was made by pressing and the heating mixture of Y2O3 (99.99%) and 2 mol% Er2O3 (99.9%) at 1000 8C for 3 h in air. The evaporation was carried out at a vacuum pressure of the order of 105 Torr. The thickness of the films was controlled to make about 500 nm using crystal thickness monitor. The films were deposited at substrate temperatures of 400 and 500 8C. The film deposited at 400 8C showed [1 0 0] orientation, whereas the film at 500 8C showed [1 1 1] orientation. As the crystallinity and CL luminance of the film at 400 8C were very poor, the experimental results of the films deposited at 500 8C are described in this paper. The ZnO thin film used as the substrate for Y2O3:Er thin film was deposited on a quartz glass by rf magnetron sputtering using ZnO target, where substrate temperature, total pressure and electric power were room temperature, 1 102 Torr and 200 W, and atmosphere was the mixture of 20% Ar and 80% O2. The ZnO film was annealed at 800 8C for 1 h in
Fig. 1. XRD curves of as-deposited and annealed ZnO thin films used as substrate for the deposition of Y2O3:Er thin film.
Ar to improve the crystallinity. Fig. 1 shows XRD curves of as-deposited and annealed films. It can be seen that the ZnO show c-axis orientation and the crystallinity is improved considerably by the annealing. All the as-deposited and annealed Y2O3:Er films were characterized by X-ray diffraction (XRD) and chathodoluminescence measurement. A continuous electron beam with a spot size of about 2 106 m2 was used to excite the Y2O3:Er phosphor films. The CL luminance and color coordinates were measured at room temperature using a luminance meter (TOPCON, BM-5A).
3. Results and discussion 3.1. On quarts glass substrates The Y2O3:Er thin films were annealed in air for 1 h at 600, 700 and 800 8C after the deposition at 500 8C on each substrate. Fig. 2 shows dependence of (a) XRD curves and (b) luminance versus anode voltage (L–V) characteristics of Y2O3:Er films deposited on quartz glass substrates on annealing temperature. It can be seen from (a) that the crystallinity of the film is improved with increasing annealing temperature. The result (b) shows that about 13 cd/m2 is obtained from the film annealed at 800 8C under excitation with 3 kV, 60 mA/cm2, and the annealing temperature dependence is small. The reason for the latter result is thought that as the quartz substrate is insulator, the film surface takes charging-up under excitation with electron beam, so the annealing effect is not reflected.
Y. Nakanishi et al. / Applied Surface Science 212–213 (2003) 815–819
Fig. 2. Dependence of (a) XRD curves and (b) L–V characteristics of Y2O3:Er thin films deposited on quartz glass substrates on annealing temperature.
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Fig. 3. Dependence of (a) XRD curves and (b) L–V characteristics of Y2O3:Er thin films deposited on ITO glass substrates on annealing temperature.
3.2. On ITO glass substrates
3.3. On c-axis-oriented ZnO thin film substrates
Fig. 3 shows dependence of (a) XRD curves and (b) L–V characteristics of the films on ITO substrates on annealing temperature. It should be noticed from (a) that the crystallinity of the films deteriorates by the annealing at higher than 700 8C. We have reported that mutual diffusion at the interface of Y2O3 and ITO is caused by the annealing even at 500 8C [12]. Therefore, the poor crystallinity of the film annealed at 700 and 800 8C shown in Fig. 3(a) seems to be due to the mutual diffusion between Y2O3 and ITO. Whereas the luminance increases with increasing annealing temperature. The reason for this fact is thought that ITO is conductive, so the charging-up on the surface is suppressed, moreover, the formation of a Er luminescence center, such as substitution of Er to Y site, is promoted by annealing at higher temperature. However, the luminance at 3 kV, 60 mA/cm2 is about 12 cd/m2 which is same as the case of the quartz substrate. This poor luminance seems to be due to the poor crystallinity.
Fig. 4 shows dependence of (a) XRD curves and (b) L–V characteristics of the films deposited on c-axisoriented ZnO thin films substrate. It should be emphasized from (a) that the film with higher crystallinity than that of the film with highest crystallinity on the quartz substrate is obtained even from as-deposited film. This fact suggest that the crystallinity of the film depends considerably on crystalline state of the substrate even if substrate is polycrystalline and amorphous. The best FWHM of 0.198 is obtained at 700 8C annealing, although nearly the same FWHM is obtained from the films as-deposited and annealed at other temperatures. It should be noticed from Fig. 4(b) that the luminance of the films is much higher than that of the films on the quartz and ITO substrates. The highest luminance of about 70 cd/m2 is obtained at 3 kV, 60 mA/cm2 excitation. These results suggest that the thin film phosphors can be used for the phosphor screen for FEDs using c-axis-oriented ZnO
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Y. Nakanishi et al. / Applied Surface Science 212–213 (2003) 815–819
Fig. 5. CL spectra of Y2O3:Er thin films deposited on the ZnO thin film substrates and annealed at several temperatures.
Fig. 4. Dependence of (a) XRD curves and (b) L–V characteristics of Y2O3:Er thin films deposited on c-axis-oriented ZnO thin films substrate on annealing temperature.
the penetration depth of the electron beam with the energy of 3 kV is smaller than 100 nm, whereas the thickness of Y2O3:Er film is about 500 nm. Therefore, it can be concluded that the CL emission obtain in this experiment is from Y2O3:Er thin films. Moreover, independence of the spectra on the annealing and substrate is based on the nature of f–f transition in trivalent rare-earth ion. The CIE coordinates of the emission are (0.32, 0.62), which is very pure green for full color display.
4. Summary film as transparent electrode in FEDs, although the luminance should be improved for practical use. In the case of ZnO film substrate, the luminance of the film annealed at 700 8C is a little higher than that of the film annealed at other temperature. The cause of this fact is not understood at present. 3.4. CL spectra Fig. 5 shows CL spectra of the Y2O3:Er thin films deposited on the ZnO film substrates under excitation with 3 kV and 60 mA/cm2. The spectra shown in the figure is the emission from f–f transition in Er ion, where main peak is by 4 S3=2 ! 4 I15=2 transition [11]. On the other hand, it is well-known that Zn-rich ZnO (ZnO:Zn) phosphor and thin film phosphor show a broad emission with a peak at around 510 nm [13]. However, the emission from the ZnO:Zn cannot be observed in the spectra shown in Fig. 5. It is because
The effect of the substrate for the structural and CL properties of Er-doped Y2O3 thin film phosphors has been investigated. The quartz, ITO and c-axis-oriented ZnO thin film were used as the substrate. The ZnO film substrate was most effective for both the structural and CL properties. It is concluded that this result is due to the good crystallinity and high conductivity of the ZnO thin film. The Y2O3:Er film on ZnO film annealed at 700 8C showed a CL luminance of about 70 cd/m2 and CIE coordinates of (0.32, 0.62). The green emission from this film is very good chromaticity, although the CL luminance should be improved.
References [1] S. Itoh, T. Watanabe, T. Yamaura, K. Yanao, in: Technical Digest of Asia Display’95, Hamamatsu, Japan, 1995, p. 617.
Y. Nakanishi et al. / Applied Surface Science 212–213 (2003) 815–819 [2] Y. Saito, S. Uemura, K. Hamaguchi, Jpn. J. Appl. Phys. 37 (1998) L346. [3] T. Komoda, Y. Honda, T. Hatai, Y. Watabe, T. Ichihara, K. Aizawa, Y. Kondo, X. Sheng, A. Kojima, N. Koshida, in: Proceedings of SID’00, Long Beach, CA, 2000, p. 428. [4] T. Kusunoki, M. Suzuki, IEEE Trans. Electron. Devices 47 (2000) 1667. [5] D.J. Robins, J. Electrochem. Soc. 127 (1980) 2694. [6] S. Itoh, T. Kimizuka, T. Tenegawa, J. Electrochem. Soc. 136 (1989) 1819. [7] J. McKittrick, G.A. Hirata, C.F. Bacalski, R. Sze, J. Mourant, K.M. Hubbard, S. Pattilo, K.V. Salazar, M. Trkula, T.R. Gosnell, J. Mater. Res. 13 (1988) 3019.
819
[8] K.G. Cho, D. Kumar, S.L. Jones, D.G. Lee, P.H. Holloway, R.K. Singh, J. Electrochem. Soc. 145 (1998) 3456. [9] Y. Nakanisi, H. Wada, H. Kominami, M. Kottaisamy, T. Aoki, Y. Hatanaka, J. Electrochem. Soc. 146 (1999) 4320. [10] G.A. Hirata, J. McKittrick, M. Avalos-Borja, J.M. Siqueiros, D. Derlin, Appl. Surf. Sci. 113–114 (1997) 509. [11] E.W. Chase, R.T. Hepplewhite, D.C. Krupka, D. Kahng, J. Appl. Phys. 40 (1969) 2512 (in Japanese). [12] Y. Nakanisi, Y. Suzuki, G. Zhou, M. Ogita, Y. Fukuda, G. Shimaoka, J. Surf. Sci. Soc. Jpn. 10 (1989) 399. [13] Y. Nakanishi, A. Miyake, H. Kominami, T. Aoki, Y. Hatanaka, G. Shimaoka, Appl. Surf. Sci. 142 (1999) 233.