Extremely Stable, High Performance Gd and Li Alloyed ZnO Thin Film Transistor by Spray Pyrolysis

Abstract

ZnO is a well-known oxide semiconductor because of its excellent electrical and optical properties due to its crystalline structure with high carrier mobility and tunable bandgap by alloying. [13,14] Although, ZnO TFT has high carrier density with crystalline structure, it has some limitations, such as instabilities. It is known that the instability of pristine ZnO is related to the grain boundary defects related to oxygen vacancy and Zn interstitial. [15] Most of pristine ZnO TFTs show negative turn-on voltage owing to its high carrier concentration, which limits the application of the TFTs to gate drivers of active-matrix organic light-emitting diode display. Metal doping in ZnO, such as In, Li, N, F, Al, Ga, Hf, La, Mg, Y, and Zr is proposed to improve the performance and/or stability. [16-23] Many ternary and quaternary metal oxide TFTs are reported to improve both stability and mobility, but the results are not promising. Adamopoulos et al. [24] reported high mobility of ZnO TFT (85 cm 2 V −1 s −1) by Li incorporation on spray pyrolyzed ZrO x gate insulator. The increase in mobility by Li incorporation is due to the increase in grain size, but due to high carrier concentration and defects in semiconductor and interface, the offstate currents are high (10 −8 A). Whereas, Park et al. [25] reported La doping in amorphous IZO TFT which reduces the oxygen deficiency and improves the stability but the mobility is low (≈4.2 cm 2 V −1 s −1). Xifeng et al. [26] reported electron mobility ≈1.94 cm 2 V −1 s −1 by Hf doping in amorphous IZO TFT, where Hf works as carrier suppressor and increases the on/off current ratio by lowering the off-currents. Tue et al. [27] reported the Zr doping in amorphous IZO TFT to control the oxygen vacancies due to its lower slandered electron potential to the off current. Jun et al. [28] reported the La doping in amorphous ZTO TFT to improve the subthreshold swing and on/off current ratio. The electronegativity, ionic radius, and dopant-oxygen bond dissociation energy are important to improve the performance and stability of oxide TFT. As the difference of electronegativity between dopants and oxygen rises, the metaloxygen bond energy increases. Besides, the low standard electrode potential (SEP) of metal ion can decrease the traps due to its binding tendency with oxygen. [29] Higher bond dissociation energy leads to the stronger metal-oxygen network and less oxygen vacancy, which helps to improve the stability of the TFTs. [30] A Gd has lower electronegativity (1.20) compare to Zn (1.65), lower SEP (−2.27 V) compare to Zn (−0.76 V) and higher bond dissociation The simultaneous doping effect of Gadolinium (Gd) and Lithium (Li) on zinc oxide (ZnO) thin-film transistor (TFT) by spray pyrolysis using a ZrO x gate insulator is reported. Li doping in ZnO increases mobility significantly, whereas the presence of Gd improves the stability of the device. The Gd ratio in ZnO is varied from 0% to 20% and the Li ratio from 0% to 10%. The optimized ZnO TFT with codoping of 5% Li and 10% Gd exhibits...

Spray‐Pyrolyzed High‐k Zirconium‐Aluminum‐Oxide Dielectric for High Performance Metal‐Oxide Thin‐Film Transistors for Low Power Displays

“…Figure 4c–e shows the hysteresis characteristics of the a‐IGZO TFTs with ZAO GIs measured by gate voltage ( V G ) sweep from −6 to +6 V (forward bias) and +6 to −6 V (reverse bias) with a drain voltage ( V D ) of 0.1 V. The a‐IGZO TFT with pristine ZAO GI exhibits the field‐effect mobility (μ FE ) of 2.67 cm 2 V −1 s −1 (as shown in Figure 4a), V TH of 2.25 V, SS of 135 mV dec −1 , I ON / I OFF ratio of 5.14 × 10 7 , and clockwise hysteresis voltage ( V H ) of 0.3 V. The origin of low mobility could be due the high density of interface traps ( D it ) between pristine ZAO and a‐IGZO layers. [ 21,45,51,52 ] The D it of pristine ZAO/a‐IGZO TFT is 1.96 × 10 12 cm −2 eV −1 . Thus, the V TH shifts toward more positive, and low μ FE , high SS, low I ON / I OFF ratio, and clockwise V H are obtained.…”

“…The highly stable and uniform a‐IGZO TFTs are achieved due to the smooth interface and low defect density at the ZAO/a‐IGZO interface for 1 cycle Ar/O 2 plasma treatment. [ 35,52–54 ] Table 3 shows the summary of reported a‐IGZO TFTs. The hysteresis, transfer, and output characteristics of a‐IGZO TFT with 4 cycles Ar/O 2 plasma‐treated ZAO GI can be seen in Figure S5a–c, Supporting Information, respectively.…”

Triple-Stack ZnO/AlZnO/YZnO Heterojunction Oxide Thin-Film Transistors by Spray Pyrolysis for High Mobility and Excellent Stability

“…Spray pyrolysis is one of the promising deposition techniques because of its low cost and large scale, uniform deposition over G10.5 glass. The other solution-processed techniques such as ink-jet printing and spin-coating have the drawbacks of the coffee-ring effect and uniformity over large area, respectively. − Among various M–O semiconductors, ZnO is a popular oxide semiconductor because of its excellent electrical and optical properties, its crystalline structure, and high carrier mobility with a tunable band gap by alloying. , Carcia et al showed the high-performance ZnO TFT based on high-k dielectric (Al 2 O 3 and HfO 2 ) . Fortunato et al showed the advantages of ZnO exhibiting faster device speed because of high electron mobility (36 cm 2 V –1 s –1 ) in the channel .…”

P‐22: Flexible La Doped ZnO TFTs and Circuits on Polyimide Substrate for Foldable Display

“…All the TFTs exhibit clear pinch of and saturation behavior. The output curve of LaZnO TFT was measured at a VGS of 5 V. [16] For the practical application of LaZnO TFTs in electronic circuits, a simple inverter was designed by connecting LaZnO TFTs. [7,8] Figure 4(c) ΔVTH as a function of out-folding cycles.…”