Solution-Processed La Alloyed ZrOx High-k Dielectric for High-Performance ZnO Thin-Film Transistors

Bukke

Jang

2020

Adv Elect Materials

Self Cite

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...

Section: Introductionmentioning

confidence: 99%

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

Bukke

Jang

2020

Adv Elect Materials

Self Cite

“…[ 17,26 ] In general, amorphous dielectric films are more favorable owing to the smoother surface, lower leakage current, and higher breakdown electric field compared to crystalline counterparts. [ 4,17,27 ] On the other hand, Zr has higher metal–oxygen (M–O) bond strength (760 kJ mol −1 ) than Al (511 kJ mol −1 ), which can enhance the M–O bonds and effectively reduces the trap states at the dielectric/semiconductor interface. [ 4,15a,28 ] In addition, compared to the vacuum‐based deposition technique, solution process (e.g., spin coating, slot‐die coating, spray pyrolysis, and inkjet printing) provides extra benefits such as low‐cost and easy chemical controllability.…”

Section: Introductionmentioning

confidence: 99%

“…[ 4,17,27 ] On the other hand, Zr has higher metal–oxygen (M–O) bond strength (760 kJ mol −1 ) than Al (511 kJ mol −1 ), which can enhance the M–O bonds and effectively reduces the trap states at the dielectric/semiconductor interface. [ 4,15a,28 ] In addition, compared to the vacuum‐based deposition technique, solution process (e.g., spin coating, slot‐die coating, spray pyrolysis, and inkjet printing) provides extra benefits such as low‐cost and easy chemical controllability. [ 2,15a,11 ] Particularly, spin coating and inkjet printing have been attracted to fabricate the MO‐TFTs.…”

Section: Introductionmentioning

confidence: 99%

“…To improve the dielectric properties of the high‐k oxides, UV/ozone treatment is investigated. [ 4,31,33 ] The UV/ozone treatment on gate dielectrics could improve the dielectric properties, but it is not possible to prevent frequency‐dependent dielectric properties. [ 4,33 ] For a good quality high‐k dielectric, the capacitance should not depend on the operating frequency.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

Islam

Hasan

et al. 2021

Adv Materials Inter

Self Cite

A high‐k, zirconium‐aluminum‐oxide (ZAO) gate insulator (GI) using low‐cost spray pyrolysis technique for large area and low power electronics is demonstrated. The high‐quality spray‐pyrolyzed ZAO GI is obtained with subsequent oxidation by eco‐friendly Ar/O2 plasma treatment. Analyses reveal that only one cycle Ar/O2 plasma treatment significantly enhances the thin‐film and dielectric properties of ZAO, exhibiting improved mass density (4.16 g cm−3), smooth surface roughness (0.32 nm), low leakage current density (2.26 × 10−6 A cm−2), high breakdown electric field (5.15 MV cm−1), and negligible frequency‐dependent capacitance. Hysteresis free, amorphous indium‐gallium‐zinc‐oxide (a‐IGZO) thin‐film transistors (TFTs) with ZAO GI exhibit a field‐effect mobility of 15.04 cm2 V−1 s−1, threshold voltage of 1.46 V, subthreshold swing of 115 mV dec−1, ION/IOFF ratio of 7.54 × 108, and negligible positive bias stress. The highly reliable a‐IGZO TFTs performances are achieved due to the significant reduction of oxygen‐related defects at the dielectric/semiconductor interface. The TFT inverter and an eleven‐stage ring oscillator have been demonstrated with ZAO/a‐IGZO TFTs, exhibiting a high voltage gain of 58, oscillation frequency of 2.43 MHz, and signal propagation delay of 18.7 ns at a supply voltage of 6 V, confirming the benefit of spray‐pyrolyzed high‐k ZAO dielectric for low power displays.

“…Next-generation displays demand low cost technology with high-performance thin-film transistors (TFTs) operated at low voltage, which should be manufactured over large area with good uniformity. Spray pyrolysis is one of the promising technologies due to its low cost and large-scale uniform deposition, compared to other solution-processed techniques such as ink-jet printing and spin coating [1][2][3][4][5]. Among various metal-oxide (M-O) semiconductors, ZnO is a well-known oxide because of its excellent electrical and optical properties due to its crystalline structure with high carrier mobility and tunable bandgap by alloying [2].…”

Section: Introductionmentioning

confidence: 99%

8‐2: Low Cost Manufacturing of AlZnO/ZnO Thin Film Transistor with High Mobility Over 80 cm2/Vs and Positive Threshold Voltage by Spray Pyrolysis

Symp Digest of Tech Papers

Ali

Islam

et al. 2021

Self Cite

We demonstrate the low‐cost AlZnO/ZnO TFT by spray pyrolysis at 350 °C. High field‐effect mobility is achieved over 80 cm2/V.s with a subthreshold slope of 123 mV/decade. The higher mobility is due to the 2D like electron gas at the interface of AlZnO/ZnO. The stack TFT shows positive threshold voltage and negligible threshold voltage shift under positive bias stress. The presence of Al‐O at the interface reduces the oxygen vacancies and improves the bias stability.