Dynamics of negative bias thermal stress-induced threshold voltage shifts in indium zinc oxide transistors: impact of the crystalline structure on the activation energy barrier

Yang

et al. 2014

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This study examined the structural, chemical, and electrical properties of solution-processed (Zn,Sn)O3 (ZTO) films with various Sn/[Zn+Sn] ratios for potential applications to large-area flat panel displays. ZTO films with a Zn-rich composition had a polycrystalline wurtzite structure. On the other hand, the Sn-rich ZTO films exhibited a rutile structure, where the Zn atom was speculated to replace the Sn site, thereby acting as an acceptor. In the intermediate composition regions (Sn/[Zn+Sn] ratio from 0.28 to 0.48), the ZTO films had an amorphous structure, even after annealing at 450 °C. The electrical transport properties and photobias stability of ZTO thin film transistors (TFTs) were also examined according to the Sn/[Zn+Sn] ratio. The optimal transport property of ZTO TFT was observed for the device with an amorphous structure at a Sn/[Zn+Sn] ratio of 0.48. The mobility, threshold voltage, subthreshold swing, and on/off current ratio were 4.3 cm(2)/(V s), 0 V, 0.4 V/decade, and 4.1 × 10(7), respectively. In contrast, the device performance for the ZTO TFTs with either a higher or lower Sn concentration suffered from low mobility and a high off-state current, respectively. The photoelectrical stress measurements showed that the photobias stability of the ZTO TFTs was improved substantially when the ZTO semiconducting films had a lower oxygen vacancy concentration and an amorphous structure. The relevant rationale is discussed based on the phototransition and subsequent migration mechanism from neutral to positively charged oxygen vacancies.

Section: Results and Discussionsupporting

confidence: 60%

Section: Resultsmentioning

confidence: 99%

Impact of the Cation Composition on the Electrical Performance of Solution-Processed Zinc Tin Oxide Thin-Film Transistors

Yang

et al. 2014

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“…The worst Δ V TH shifts were observed for the In 2 O y TFTs: Δ V TH values were 0.13 and −0.39 V after the duration of PBS and NBS for 3,600 s, respectively. Considering that the In 2 O y film contains the largest V O related peak of 12.5%, the conversion from donor-like V O 2+ to V O by capturing two free electrons under the PBS condition would be responsible for the positive V TH shift as follows ( V O 2+ + 2 e – → V O ). − The opposite negative V TH shift under the NBS condition can be described by the reverse reaction due to the downward movement of the quasi-Fermi level ( E F ). The additional absorption and desorption of O 2 gas (or desorption and adsorption of moisture) cannot be ruled out as an origin for the positive and negative V TH shift under PBS and NBS duration, respectively, because the fabricated devices were not encapsulated by the suitable passivation layer. , Recently, it has been reported that V TH instability under the NBS condition can be amplified due to carbon-monoxide (CO) related impurities, which can be seen in the case of high-mobility oxide semiconductors containing Sn cations .…”

Section: Results and Discussionmentioning

confidence: 99%

High-Performance Thin-Film Transistor with Atomic Layer Deposition (ALD)-Derived Indium–Gallium Oxide Channel for Back-End-of-Line Compatible Transistor Applications: Cation Combinatorial Approach

Hur

Yoon

et al. 2022

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In this paper, the feasibility of an indium−gallium oxide (In 2(1-x) Ga 2x O y ) film through combinatorial atomic layer deposition (ALD) as an alternative channel material for back-endof-line (BEOL) compatible transistor applications is studied. The microstructure of random polycrystalline In 2 O y with a bixbyite structure was converted to the amorphous phase of In 2(1−x) Ga 2x O y film under thermal annealing at 400 °C when the fraction of Ga is ≥29 at. %. In contrast, the enhancement in the orientation of the (222) face and subsequent grain size was observed for the In 1.60 Ga 0.40 O y film with the intermediate Ga fraction of 20 at. %. The suitability as a channel layer was tested on the 10-nm-thick HfO 2 gate oxide where the natural length was designed to meet the requirement of short channel devices with a smaller gate length (<100 nm). The In 1.60 Ga 0.40 O y thin-film transistors (TFTs) exhibited the high field-effect mobility (μ FE ) of 71.27 ± 0.98 cm 2 /(V s), low subthreshold gate swing (SS) of 74.4 mV/decade, threshold voltage (V TH ) of −0.3 V, and I ON/OFF ratio of >10 8 , which would be applicable to the logic devices such as peripheral circuit of heterogeneous DRAM. The in-depth origin for this promising performance was discussed in detail, based on physical, optical, and chemical analysis.

“…As shown in Figure S6, the stability enhancement of OSL/a-IGZO TFTs was observed with NBTS and NBIS results. As a result, the bias-, illumination-, and temperature-induced behaviors of V O were enhanced by the OSL. , …”

Section: Results and Discussionmentioning

confidence: 99%

“…As a result, the bias-, illumination-, and temperature-induced behaviors of V O were enhanced by the OSL. 38,39 We conducted HR-TEM image, CPS scan profile, and EDS mapping analyses to verify the role of Hf in the OSL for the OSL/a-IGZO TFT. The thicknesses of the a-IGZO film layer and OSL in the OSL/a-IGZO TFT were 17 and 33 nm, respectively, as shown in Figure 5a.…”

Section: Experimental Methodsmentioning

confidence: 99%

Multifunctional Oxygen Scavenger Layer for High-Performance Oxide Thin-Film Transistors with Low-Temperature Processing

Yoo

et al. 2021

In this study, the oxygen scavenger layer (OSL) is proposed as a back channel in the bilayer channel to enhance both the electrical characteristics and stability of an amorphous indium–gallium–zinc oxide thin-film transistor (a-IGZO TFT) and also to enable its fabrication at low temperature. The OSL is a hafnium (Hf)-doped a-IGZO channel layer deposited by radio-frequency magnetron cosputtering. Amorphous IGZO TFTs with the OSL, even if annealed at a low temperature (200 °C), exhibited improved electrical characteristics and stability under positive bias temperature stress (PBTS) compared to those without the OSL, specifically in terms of field-effect mobility (31.08 vs 9.25 cm2/V s), on/off current ratio (1.73 × 1010 vs 8.68 × 108), and subthreshold swing (0.32 vs 0.43 V/decade). The threshold voltage shift under PBTS at 50 °C for 10,000 s decreased from 9.22 to 2.31 V. These enhancements are attributed to Hf in the OSL, which absorbs oxygen ions from the a-IGZO front channel near the interface between a-IGZO and the OSL.