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Threshold voltage shift by controlling Ga in solution processed Si–In–Zn–O thin film transistors
Thin Solid Films 520 (2012) 3774–3777
Contents lists available at SciVerse ScienceDirect
Thin Solid Films journal homepage: www.elsevier.com/locate/tsf
Threshold voltage shift by controlling Ga in solution processed Si–In–Zn–O thin film transistors Jun Young Choi a, SangSig Kim a, Sang Yeol Lee b,⁎ a b
Department of Electrical Engineering and Institute for Nano Science, Korea University, Seoul 136-701, Republic of Korea Department of Semiconductor Engineering, Cheongju University, Cheonju, Chungbuk, 360-764, Republic of Korea
a r t i c l e
i n f o
Available online 29 November 2011 Keywords: Zinc oxide Chemical deposition from solution Threshold voltage Low temperature
a b s t r a c t The threshold voltage change of solution processed gallium–silicon–indium–zinc oxide (GSIZO) thin film transistors (TFTs) annealed at 200 °C has been investigated depending on gallium ratio. GSIZO thin films were formed with various gallium ratios from 0.01 to 1 M ratio. The 30 nm-thick GSIZO film exhibited optimized electrical characteristics, such as field effect mobility (μFE) of 2.2 × 10 − 2 cm 2/V·s, subthreshold swing (S.S) of 0.11 V/dec, and on/off current ratio (Ion/off) of above 105. The variation of gallium metal cation has an effect on the threshold voltage (Vth) and the field effect mobility (μFE). The Vth was shifted toward positive direction from − 5.2 to − 0.4 V as increasing gallium ratio, and μFE was decreased from 2.2 × 10 − 2 to 5 × 10 − 3 cm 2/V s. These results indicated that gallium was acted as carrier suppressor by degenerating oxygen vacancy. The electrical property of GSIZO TFTs has been analyzed as a function of the gallium ratio in SIZO system, and it clearly showed that variation of gallium contents could change on the performance of TFTs. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Amorphous oxide semiconductors (AOSs) have been a promising candidate for the active channel layer of thin film transistors (TFTs) used in the next generation flat panel display because AOSs have high transparency due to wide band gap (>3 eV), excellent environmental stability, and high mobility. Zn-based oxide semiconductors have been widely investigated as an active channel layer in thin film transistors (TFTs). Polycrystalline oxides semiconductors show low carrier mobility problem due to the carrier scattering at grain boundary, but AOSs including post-transition-metal cations do not have this issue because the direct orbital overlap between s orbitals of neighboring metal cations are larger than that of polycrystalline semiconductors [1–4]. Therefore, it is important to have amorphous phase in TFTs for high carrier mobility. ZnO-based oxide TFTs are promising candidate for the flat panel display applications since it can be used in amorphous phase on glass and flexible substrates. Most of recently reported oxidebased TFTs were fabricated by using vacuum deposition process, such as RF magnetron sputtering, pulsed laser deposition and chemical vapor deposition, which were high cost deposition method [5,6]. By contrast, a solution-based deposition offers a simple, low-cost and large-area deposition method as an alternative to
⁎ Corresponding author. Tel.: + 82 43 229 8534; fax: + 82 43 229 8461. E-mail address: [email protected] (S.Y. Lee). 0040-6090/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2011.10.212
vacuum deposition technique of physical vapor deposition, chemical vapor deposition or pulsed laser deposition [7]. To obtain better transfer characteristics of solution-processed TFTs, TFTs require high annealing temperature. However, it is possible to decrease annealing temperature by controlling the formation of oxygen-lattice. Gallium doping allows the amorphous oxide semiconductors to achieve metal–oxide lattice structures at low temperature [8]. Also, silicon metal cations have higher M–O bonding energy (775 kJ/mol) than indium (470 kJ/mol) and zinc (385 kJ/ mol) [3]. Therefore, silicon and gallium have an effect on the degeneration of the oxygen vacancy in the films, which is the origin of majority carrier [9]. In this study, GSIZO TFTs have been fabricated by solution-process at low temperature to control threshold voltage. The role of gallium has been analyzed by observing the threshold voltage shift of GSIZO TFTs. 2. Experimental procedures To obtain GSIZO solution precursor, silicon tetra acetate [Si (OCOCH3)4], indium nitrate hydrate [In (NO3)3·xH2O], and zinc acetate dihydrate [Zn (CH3COO)2·2H2O] were dissolved into 2methoxyethanol [C3H8O2] which was used as solvent. Then, gallium nitrate hydrate [Ga (NO3)3 H2O] was dissolved in the SIZO precursor with molar ratio from 0.01 to 1. Mono-ethanolamine was added as stabilizer to increase solution solubility, and then it was stirred at 60 °C for 24 h to form GSIZO precursor. The GSIZO solution was filtered through a 0.5 μm syringe filter. The GSIZO precursor was deposited by spin-coating on the SiO2
J.Y. Choi et al. / Thin Solid Films 520 (2012) 3774–3777
Fig. 1. Device structure of solution processed bottom-gate and top-contact oxidesemiconductor-based TFTs.
(200 nm)/heavily doped p-type Si wafer to obtain active channel layer at room temperature and atmospheric pressure. The spin speed was maintained at 4500 rpm to form uniform thin film thickness. Next, the soft baking for 5 min was performed to remove residual organic materials in 2-methoxyethanol. To improve the film quality, the annealing process was performed in furnace at 200 °C for 2 h in atmosphere. The patterning of active channel layer was performed by the conventional photolithography and wet etching process. The width and length of active channel layer were 250 and 50 μm, respectively. The source/drain electrodes were patterned by lift-off process and thermal-evaporation deposition of Ti/Au. The schematic configuration of the TFT has been shown in Fig. 1. The structure properties of GSIZO layers were characterized by X-ray diffraction (XRD). To analyze the change in the chemical bonding states of oxygen vacancy of GSIZO, X-ray photoemission spectroscopy (XPS) was conducted. The electrical characteristics of the GSIZO TFTs were measured using semiconductor parameter analyzer. 3. Results and discussion As shown in Fig. 2, XRD of GSIZO shows broad peak which clearly indicates amorphous phase. Some metal cation elements in active channel layer make an amorphous phase or prevent their columnar growth. Therefore, the metal elements act as a diffusion suppressor of ZnO-based TFTs because they are heavy and slow in terms of diffusion [10,11]. Amorphous phase of an active channel layer is an important point because carrier transport in TFT's channel layer is considerably affected by phase structure of the channel layer. The (n-1)d 10ns 0 electronic configuration of metal elements in oxide semiconductor, such as ZnO, In-ZnO, and Si–In–
3775
ZnO, has the possibility to form electron transport paths through the series of s orbitals. Fig. 3 shows XPS spectra of GSIZO O1s peak around 530 eV corresponding to the O1s core level. The O1s XPS peaks of GSIZO films were calibrated by taking C1s reference at 284.25 eV. The O1s peak can be deconvoluted into three binding energy peaks. The low binding energy (O1) at 529.24 eV peak can be attributed to O 2− ions surrounded by Si, Zn, In and Ga atoms in GSIZO systems, and the medium binding energy (OII) component centered at 530.68 eV peak is associated with oxygen-deficient regions within the GSIZO compound. Therefore, the intensity change in the components can be explained by the variation in the concentration of oxygen vacancy. The higher binding energy (OIII) at 531.75 eV peak is related to loosely bound oxygen on the surface of films, such as \CO3, adsorbed H2O, and adsorbed O2[12,13]. Generally, OII related-oxygen vacancies provide free electrons in the GSIZO TFTs active layers [14,15]. The OII/Otot ratio decreases as increasing gallium doping contents. Because gallium has low standard electrode potential (SEP), gallium ion can form strong chemical bonds with oxygen [8]. This result indicated that the oxygen vacancies as electron charge carrier were reduced by increasing gallium contents in GSIZO systems. So, gallium in GSIZO active channel layer decreases carrier concentration. To investigate the electrical properties, the transfer characteristics and the device parameters of GSIZO TFTs have been measured by varying gallium contents as shown in Fig. 4 and listed in Table 1. It is interesting to note that the threshold voltage is shifted toward positive direction from −5.2 to − 0.4 V when gallium ratio is increased in active channel layers. Because the gallium metal cation has strong chemical binding with oxygen due to low SEP value, the Vth shifts toward positive direction as increasing gallium ratio in GSIZO film, which indicates that the carrier concentrations are decreased as increasing gallium ratio [8]. TFTs based on GSIZO films annealed at 200 °C show the decrease of on-current as increasing gallium contents. Field effect mobility (μFE) was decreased from 2.2 × 10 − 2 to 5 × 10 − 3 with the increase of gallium molar ratio from 0.01 to 1. Addition of gallium atoms in GSIZO active layer degenerates oxygen vacancies since gallium can act as a carrier suppressor, and consequently it decreased the on-current of the TFTs as increasing gallium contents. The carrier concentration was calculated by the following formulas Ncp ¼
C i V on qt c
where Ci, q, and tc are the gate dielectrics capacitance per area, elementary charge, and the channel thickness, respectively [16]. The carrier concentration in GSIZO systems was decreased from
Fig. 2. XRD patterns of the GSIZO film with increasing Ga contents (a) 0.01 wt.% (b) 0.5 wt.% (c) 1 wt.%.
3776
J.Y. Choi et al. / Thin Solid Films 520 (2012) 3774–3777
Ga :Si : In : Zn molar ratio
Deconvolution
0.01 : 0.05 : 5: 1
0.5 : 0.05 : 5 :1
1 : 0.05 :5 :1
OI
47.7
OII
43.8
OIII
8.3
OI
51.8
OII
39.9
OIII
8.3
OI
55.4
OII
39.7
OIII
4.9
Intensity (arb. unit.)
(a)
0.01 : 0.05 : 5 : 1
526
0.5: 0.05 : 5: 1
(b)
528
530
532
534
536
Binding Energy (eV)
1 : 0.05 : 5: 1
(c) Intensity (arb. unit.)
Intensity (arb. unit.)
Area(%)
526
528
530
532
534
536
526
Binding Energy (eV)
528
530
532
534
536
Binding Energy (eV)
Current(A)
Fig. 3. XPS spectra of O1s peak for solution-processed of GSIZO thin film for Ga:Si:In:Zn ratio of (a)0.01:0.05:5:1 (b)0.5:0.05:5:1 (c)1:0.05:5:1.
10
-7
10
-9
10
-11
10
-13
2.159 × 10 17 to 2.15 × 10 16 because it is related with the oxygen vacancy which can be controlled by the addition of gallium in GSIZO system.
0.01 mole 0.05 mole 0.2 mole 0.5 mole 1 mole
-40
-30
-20
4. Conclusions
-10
0
10
20
30
40
Gate Voltage(V) Fig. 4. Drain current gate-voltage transfer characteristics of solution-processed GSIZO TFTs.
In summary, we have investigated the effect of Ga in the SIZO on the performance of TFT fabricated by solution-process and annealed at 200 °C. Because Ga in the SIZO system acts as good carrier suppressor due to low SEP value, the transfer characteristic shows the decrease of on-current and the positive shift of Vth from − 5.2 to −0.4 V as increasing gallium ratio. Also, the S.S of 0.11 V/decade, Ion/off ratio of 6.4 × 10 5 and μFE of 2.2 × 10 − 2 were observed. The XRD patterns indicated that GSIZO was formed in amorphous phase. The shift of threshold voltage in GSIZO system is mainly due to the control of oxygen vacancies by the addition of Ga into GSIZO. Solution processed GSIZO shows the possibility for practical applications, like flexible displays especially due to low annealing temperature of 200 °C. References
Table 1 Electrical parameters of GSIZO transistors with different Ga composition ratio. Ga:Si:In:Zn
Vth (V)
Ion/off current ratio
μFE (cm2 V− 1 S− 1)
Subthreshold swing (V/decade)
Nt (cm− 2)
0.01:0.5:5:1 0.1:0.5:5:1 0.2:0.5:5:1 0.5:0.5:5:1 1:0.5:5:1
5.20 3.14 1.70 − 0.6 − 0.4
6.4 × 105 1.1 × 104 7.9 × 103 7.3 × 103 3.6 × 103
0.022 0.027 0.015 0.006 0.005
0.61 0.72 0.90 0.41 0.11
2.15 × 1017 2.05 × 1017 1.40 × 1017 7.01 × 1016 2.15 × 1016
[1] S. Narushima, H. Mizoguchi, K. Shimizu, K. Ueda, H. Ohta, M. Hirano, T. Kamiya, H. Hosono, Adv. Mater. 15 (2003) 1409. [2] E.M.C. Fortunato, P.M.C. Barquinha, A.M.B.G. Pimentel, A.M.F. Gonçalves, A.J.S. Marques, R.F.P. Martins, L.M.N. Pereira, Appl. Phys. Lett. 85 (2004) 2541. [3] E. Chong, S.H. Kim, S.Y. Lee, Appl. Phys. Lett. 97 (2010) 252112. [4] K. Nomura, T. kamiya, H. Ohta, T. Uruga, M. Hirano, H. Hosono, Phys. Rev. B 75 (2007) 035212. [5] W.B. Jackson, R.L. Hoffman, G.S. Herman, Appl. Phys. Lett. 87 (2005) 193503. [6] J.J. Chen, M.H. Yu, W.L. Zhou, K. Sun, L.M. Wang, Appl. Phys. Lett. 87 (2005) 173119. [7] D. Redinger, V. Subramanian, IEEE Trans. Electron Devices 54 (2007) 1301. [8] S. Jeong, Y.-G. Ha, J. Moon, A. Facchetti, T.J. Marks, Adv. Mater. 22 (2010) 1346. [9] E. Chong, Y.S. Chun, S.Y. Lee, Appl. Phys. Lett. 97 (2010) 102102.
J.Y. Choi et al. / Thin Solid Films 520 (2012) 3774–3777 [10] A.K. Varshneya, Fundamentals of inorganic Glassed, Academic Press, Inc., New York, 1993. [11] J.W. He, C.D. Bai, K.W. Xu, N.S. Hu, Surf. Coat.Technol. 74 (1995) 387. [12] W.H. Jeong, G.H. Kim, H.S. Shin, B.D. Ahn, H.J. Kim, M.-K. Ryu, K.-B. Park, J.-B. Seon, S.Y. Lee, Appl. Phys. Lett. 96 (2010) 093503. [13] M.N. Islam, T.B. Ghosh, K.L. Chopra, H.N. Acharya, Thin Solid Films 280 (1996) 20.
3777
[14] P.F. Carcia, R.S. McLean, M.H. Reilly, G. Nunes Jr., Appl. Phys. Lett. 82 (2003) 1117. [15] R. Martins, P. Barquinha, I. Ferreira, L. Pereira, G. Goncalves, E. Fortunato, J. Appl. Phys. 101 (2007) 044505. [16] J.-S. Park, J.K. Jeong, Y.-G. Mo, H.D. Kim, C.-J. Kim, Appl. Phys. Lett. 93 (2008) 033513.
Contents lists available at SciVerse ScienceDirect
Thin Solid Films journal homepage: www.elsevier.com/locate/tsf
Threshold voltage shift by controlling Ga in solution processed Si–In–Zn–O thin film transistors Jun Young Choi a, SangSig Kim a, Sang Yeol Lee b,⁎ a b
Department of Electrical Engineering and Institute for Nano Science, Korea University, Seoul 136-701, Republic of Korea Department of Semiconductor Engineering, Cheongju University, Cheonju, Chungbuk, 360-764, Republic of Korea
a r t i c l e
i n f o
Available online 29 November 2011 Keywords: Zinc oxide Chemical deposition from solution Threshold voltage Low temperature
a b s t r a c t The threshold voltage change of solution processed gallium–silicon–indium–zinc oxide (GSIZO) thin film transistors (TFTs) annealed at 200 °C has been investigated depending on gallium ratio. GSIZO thin films were formed with various gallium ratios from 0.01 to 1 M ratio. The 30 nm-thick GSIZO film exhibited optimized electrical characteristics, such as field effect mobility (μFE) of 2.2 × 10 − 2 cm 2/V·s, subthreshold swing (S.S) of 0.11 V/dec, and on/off current ratio (Ion/off) of above 105. The variation of gallium metal cation has an effect on the threshold voltage (Vth) and the field effect mobility (μFE). The Vth was shifted toward positive direction from − 5.2 to − 0.4 V as increasing gallium ratio, and μFE was decreased from 2.2 × 10 − 2 to 5 × 10 − 3 cm 2/V s. These results indicated that gallium was acted as carrier suppressor by degenerating oxygen vacancy. The electrical property of GSIZO TFTs has been analyzed as a function of the gallium ratio in SIZO system, and it clearly showed that variation of gallium contents could change on the performance of TFTs. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Amorphous oxide semiconductors (AOSs) have been a promising candidate for the active channel layer of thin film transistors (TFTs) used in the next generation flat panel display because AOSs have high transparency due to wide band gap (>3 eV), excellent environmental stability, and high mobility. Zn-based oxide semiconductors have been widely investigated as an active channel layer in thin film transistors (TFTs). Polycrystalline oxides semiconductors show low carrier mobility problem due to the carrier scattering at grain boundary, but AOSs including post-transition-metal cations do not have this issue because the direct orbital overlap between s orbitals of neighboring metal cations are larger than that of polycrystalline semiconductors [1–4]. Therefore, it is important to have amorphous phase in TFTs for high carrier mobility. ZnO-based oxide TFTs are promising candidate for the flat panel display applications since it can be used in amorphous phase on glass and flexible substrates. Most of recently reported oxidebased TFTs were fabricated by using vacuum deposition process, such as RF magnetron sputtering, pulsed laser deposition and chemical vapor deposition, which were high cost deposition method [5,6]. By contrast, a solution-based deposition offers a simple, low-cost and large-area deposition method as an alternative to
⁎ Corresponding author. Tel.: + 82 43 229 8534; fax: + 82 43 229 8461. E-mail address: [email protected] (S.Y. Lee). 0040-6090/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2011.10.212
vacuum deposition technique of physical vapor deposition, chemical vapor deposition or pulsed laser deposition [7]. To obtain better transfer characteristics of solution-processed TFTs, TFTs require high annealing temperature. However, it is possible to decrease annealing temperature by controlling the formation of oxygen-lattice. Gallium doping allows the amorphous oxide semiconductors to achieve metal–oxide lattice structures at low temperature [8]. Also, silicon metal cations have higher M–O bonding energy (775 kJ/mol) than indium (470 kJ/mol) and zinc (385 kJ/ mol) [3]. Therefore, silicon and gallium have an effect on the degeneration of the oxygen vacancy in the films, which is the origin of majority carrier [9]. In this study, GSIZO TFTs have been fabricated by solution-process at low temperature to control threshold voltage. The role of gallium has been analyzed by observing the threshold voltage shift of GSIZO TFTs. 2. Experimental procedures To obtain GSIZO solution precursor, silicon tetra acetate [Si (OCOCH3)4], indium nitrate hydrate [In (NO3)3·xH2O], and zinc acetate dihydrate [Zn (CH3COO)2·2H2O] were dissolved into 2methoxyethanol [C3H8O2] which was used as solvent. Then, gallium nitrate hydrate [Ga (NO3)3 H2O] was dissolved in the SIZO precursor with molar ratio from 0.01 to 1. Mono-ethanolamine was added as stabilizer to increase solution solubility, and then it was stirred at 60 °C for 24 h to form GSIZO precursor. The GSIZO solution was filtered through a 0.5 μm syringe filter. The GSIZO precursor was deposited by spin-coating on the SiO2
J.Y. Choi et al. / Thin Solid Films 520 (2012) 3774–3777
Fig. 1. Device structure of solution processed bottom-gate and top-contact oxidesemiconductor-based TFTs.
(200 nm)/heavily doped p-type Si wafer to obtain active channel layer at room temperature and atmospheric pressure. The spin speed was maintained at 4500 rpm to form uniform thin film thickness. Next, the soft baking for 5 min was performed to remove residual organic materials in 2-methoxyethanol. To improve the film quality, the annealing process was performed in furnace at 200 °C for 2 h in atmosphere. The patterning of active channel layer was performed by the conventional photolithography and wet etching process. The width and length of active channel layer were 250 and 50 μm, respectively. The source/drain electrodes were patterned by lift-off process and thermal-evaporation deposition of Ti/Au. The schematic configuration of the TFT has been shown in Fig. 1. The structure properties of GSIZO layers were characterized by X-ray diffraction (XRD). To analyze the change in the chemical bonding states of oxygen vacancy of GSIZO, X-ray photoemission spectroscopy (XPS) was conducted. The electrical characteristics of the GSIZO TFTs were measured using semiconductor parameter analyzer. 3. Results and discussion As shown in Fig. 2, XRD of GSIZO shows broad peak which clearly indicates amorphous phase. Some metal cation elements in active channel layer make an amorphous phase or prevent their columnar growth. Therefore, the metal elements act as a diffusion suppressor of ZnO-based TFTs because they are heavy and slow in terms of diffusion [10,11]. Amorphous phase of an active channel layer is an important point because carrier transport in TFT's channel layer is considerably affected by phase structure of the channel layer. The (n-1)d 10ns 0 electronic configuration of metal elements in oxide semiconductor, such as ZnO, In-ZnO, and Si–In–
3775
ZnO, has the possibility to form electron transport paths through the series of s orbitals. Fig. 3 shows XPS spectra of GSIZO O1s peak around 530 eV corresponding to the O1s core level. The O1s XPS peaks of GSIZO films were calibrated by taking C1s reference at 284.25 eV. The O1s peak can be deconvoluted into three binding energy peaks. The low binding energy (O1) at 529.24 eV peak can be attributed to O 2− ions surrounded by Si, Zn, In and Ga atoms in GSIZO systems, and the medium binding energy (OII) component centered at 530.68 eV peak is associated with oxygen-deficient regions within the GSIZO compound. Therefore, the intensity change in the components can be explained by the variation in the concentration of oxygen vacancy. The higher binding energy (OIII) at 531.75 eV peak is related to loosely bound oxygen on the surface of films, such as \CO3, adsorbed H2O, and adsorbed O2[12,13]. Generally, OII related-oxygen vacancies provide free electrons in the GSIZO TFTs active layers [14,15]. The OII/Otot ratio decreases as increasing gallium doping contents. Because gallium has low standard electrode potential (SEP), gallium ion can form strong chemical bonds with oxygen [8]. This result indicated that the oxygen vacancies as electron charge carrier were reduced by increasing gallium contents in GSIZO systems. So, gallium in GSIZO active channel layer decreases carrier concentration. To investigate the electrical properties, the transfer characteristics and the device parameters of GSIZO TFTs have been measured by varying gallium contents as shown in Fig. 4 and listed in Table 1. It is interesting to note that the threshold voltage is shifted toward positive direction from −5.2 to − 0.4 V when gallium ratio is increased in active channel layers. Because the gallium metal cation has strong chemical binding with oxygen due to low SEP value, the Vth shifts toward positive direction as increasing gallium ratio in GSIZO film, which indicates that the carrier concentrations are decreased as increasing gallium ratio [8]. TFTs based on GSIZO films annealed at 200 °C show the decrease of on-current as increasing gallium contents. Field effect mobility (μFE) was decreased from 2.2 × 10 − 2 to 5 × 10 − 3 with the increase of gallium molar ratio from 0.01 to 1. Addition of gallium atoms in GSIZO active layer degenerates oxygen vacancies since gallium can act as a carrier suppressor, and consequently it decreased the on-current of the TFTs as increasing gallium contents. The carrier concentration was calculated by the following formulas Ncp ¼
C i V on qt c
where Ci, q, and tc are the gate dielectrics capacitance per area, elementary charge, and the channel thickness, respectively [16]. The carrier concentration in GSIZO systems was decreased from
Fig. 2. XRD patterns of the GSIZO film with increasing Ga contents (a) 0.01 wt.% (b) 0.5 wt.% (c) 1 wt.%.
3776
J.Y. Choi et al. / Thin Solid Films 520 (2012) 3774–3777
Ga :Si : In : Zn molar ratio
Deconvolution
0.01 : 0.05 : 5: 1
0.5 : 0.05 : 5 :1
1 : 0.05 :5 :1
OI
47.7
OII
43.8
OIII
8.3
OI
51.8
OII
39.9
OIII
8.3
OI
55.4
OII
39.7
OIII
4.9
Intensity (arb. unit.)
(a)
0.01 : 0.05 : 5 : 1
526
0.5: 0.05 : 5: 1
(b)
528
530
532
534
536
Binding Energy (eV)
1 : 0.05 : 5: 1
(c) Intensity (arb. unit.)
Intensity (arb. unit.)
Area(%)
526
528
530
532
534
536
526
Binding Energy (eV)
528
530
532
534
536
Binding Energy (eV)
Current(A)
Fig. 3. XPS spectra of O1s peak for solution-processed of GSIZO thin film for Ga:Si:In:Zn ratio of (a)0.01:0.05:5:1 (b)0.5:0.05:5:1 (c)1:0.05:5:1.
10
-7
10
-9
10
-11
10
-13
2.159 × 10 17 to 2.15 × 10 16 because it is related with the oxygen vacancy which can be controlled by the addition of gallium in GSIZO system.
0.01 mole 0.05 mole 0.2 mole 0.5 mole 1 mole
-40
-30
-20
4. Conclusions
-10
0
10
20
30
40
Gate Voltage(V) Fig. 4. Drain current gate-voltage transfer characteristics of solution-processed GSIZO TFTs.
In summary, we have investigated the effect of Ga in the SIZO on the performance of TFT fabricated by solution-process and annealed at 200 °C. Because Ga in the SIZO system acts as good carrier suppressor due to low SEP value, the transfer characteristic shows the decrease of on-current and the positive shift of Vth from − 5.2 to −0.4 V as increasing gallium ratio. Also, the S.S of 0.11 V/decade, Ion/off ratio of 6.4 × 10 5 and μFE of 2.2 × 10 − 2 were observed. The XRD patterns indicated that GSIZO was formed in amorphous phase. The shift of threshold voltage in GSIZO system is mainly due to the control of oxygen vacancies by the addition of Ga into GSIZO. Solution processed GSIZO shows the possibility for practical applications, like flexible displays especially due to low annealing temperature of 200 °C. References
Table 1 Electrical parameters of GSIZO transistors with different Ga composition ratio. Ga:Si:In:Zn
Vth (V)
Ion/off current ratio
μFE (cm2 V− 1 S− 1)
Subthreshold swing (V/decade)
Nt (cm− 2)
0.01:0.5:5:1 0.1:0.5:5:1 0.2:0.5:5:1 0.5:0.5:5:1 1:0.5:5:1
5.20 3.14 1.70 − 0.6 − 0.4
6.4 × 105 1.1 × 104 7.9 × 103 7.3 × 103 3.6 × 103
0.022 0.027 0.015 0.006 0.005
0.61 0.72 0.90 0.41 0.11
2.15 × 1017 2.05 × 1017 1.40 × 1017 7.01 × 1016 2.15 × 1016
[1] S. Narushima, H. Mizoguchi, K. Shimizu, K. Ueda, H. Ohta, M. Hirano, T. Kamiya, H. Hosono, Adv. Mater. 15 (2003) 1409. [2] E.M.C. Fortunato, P.M.C. Barquinha, A.M.B.G. Pimentel, A.M.F. Gonçalves, A.J.S. Marques, R.F.P. Martins, L.M.N. Pereira, Appl. Phys. Lett. 85 (2004) 2541. [3] E. Chong, S.H. Kim, S.Y. Lee, Appl. Phys. Lett. 97 (2010) 252112. [4] K. Nomura, T. kamiya, H. Ohta, T. Uruga, M. Hirano, H. Hosono, Phys. Rev. B 75 (2007) 035212. [5] W.B. Jackson, R.L. Hoffman, G.S. Herman, Appl. Phys. Lett. 87 (2005) 193503. [6] J.J. Chen, M.H. Yu, W.L. Zhou, K. Sun, L.M. Wang, Appl. Phys. Lett. 87 (2005) 173119. [7] D. Redinger, V. Subramanian, IEEE Trans. Electron Devices 54 (2007) 1301. [8] S. Jeong, Y.-G. Ha, J. Moon, A. Facchetti, T.J. Marks, Adv. Mater. 22 (2010) 1346. [9] E. Chong, Y.S. Chun, S.Y. Lee, Appl. Phys. Lett. 97 (2010) 102102.
J.Y. Choi et al. / Thin Solid Films 520 (2012) 3774–3777 [10] A.K. Varshneya, Fundamentals of inorganic Glassed, Academic Press, Inc., New York, 1993. [11] J.W. He, C.D. Bai, K.W. Xu, N.S. Hu, Surf. Coat.Technol. 74 (1995) 387. [12] W.H. Jeong, G.H. Kim, H.S. Shin, B.D. Ahn, H.J. Kim, M.-K. Ryu, K.-B. Park, J.-B. Seon, S.Y. Lee, Appl. Phys. Lett. 96 (2010) 093503. [13] M.N. Islam, T.B. Ghosh, K.L. Chopra, H.N. Acharya, Thin Solid Films 280 (1996) 20.
3777
[14] P.F. Carcia, R.S. McLean, M.H. Reilly, G. Nunes Jr., Appl. Phys. Lett. 82 (2003) 1117. [15] R. Martins, P. Barquinha, I. Ferreira, L. Pereira, G. Goncalves, E. Fortunato, J. Appl. Phys. 101 (2007) 044505. [16] J.-S. Park, J.K. Jeong, Y.-G. Mo, H.D. Kim, C.-J. Kim, Appl. Phys. Lett. 93 (2008) 033513.