Ambient Constancy of Passivation-Free Ultra-Thin Zinc Tin Oxide Thin Film Transistor

Abstract

An ultra-thin (5 nm-thick), unpassivated zinc tin oxide (ZTO) thin-film transistor TFT, fabricated with solution process, exhibits a good field-effect mobility (13 ∼ 14 cm 2 /Vs), small subthreshold swing (∼0.30 V/dec.) and high on/off current ratio (∼10 8 ). The field-effect mobility can be further enhanced by increasing the ZTO thickness to 12 nm and 22 nm. Furthermore, I D -V G characteristics of the 5 nm-thick ZTO TFT remain unaffected, regardless of working in air (60% relative humidity), vacuum or dry O 2 atmosphere. The dissimilar TFT characteristics are discussed in terms of oxygen deficiency content, as well as the Fermi level position (E F to E C ) for ZTO of various thicknesses to explain the moisture immunity of the 5 nm-thick solution-processed ZTO TFT. © The Author Zinc oxide-based thin film transistors (TFTs) have been applied in a wide range of electronic circuits, such as flat-panel displays, light emitting diodes and charge trapping non-volatile memory.1-2 Among them, zinc tin oxide (ZTO) TFT that is indium-and gallium-free has gained an advantage because of the low-cost competition.3-5 In addition, the solution process has attracted much attention for TFT fabrication since it enables process simplification and high throughput even for large-area displays, thereby providing a reduction in manufacturing costs for flat-panel displays.6 Furthermore, the stability and reliability of TFTs has been intensively studied in recent years, which are one of the most important issues for their practical application. 7-8Thus, our previous study had investigated transistor characteristics and bias stability with and without light illumination for solution processed ultra-thin ZTO TFTs without passivation.9 However, for unpassivated devices, the back surface of metal oxides are sensitive to the ambiance (oxygen, water and/or dipole molecules), which may be the dominant factors affecting the threshold voltage (V th ).10-12 The comparison of back and front channel conduction in ZnO-based TFT, using ionic liquid and SiO 2 dielectrics, respectively, has also been reported. 13 On the other hand, the effect of active layer thickness on the electrical performance of oxide TFTs has been investigated for oxide TFTs, [14][15][16] including solution processed ZTO. 17 However, not much attention has been paid on the characteristics of TFTs with ultrathin active oxide films (less than 10 nm). In addition, oxygen vacancy content in ZTO may be thickness dependent and will influence the ambient effect as well. In this work, we report the ZTO thickness dependence of oxygen deficiency content and its impact on electrical characteristics with different ambiances for solution processed ZTO TFTs. The relationship between oxygen deficiency content and adsorption of water molecules by comparing the TFT performance in air (relative humidity of 60%), vacuum (3 × 10 −5 torr) and dry O 2 (760 torr) atmosphere for varying ZTO thickness are investigated in detail. ExperimentalThe bottom-gate, top contact ZTO TFTs were fabricated on ptype ...

High‐Performance Zinc Tin Oxide TFTs with Active Layers Deposited by Atomic Layer Deposition

“…[59] In addition to improving the switching and turn-on properties of the devices, optimizing substrate preparation and the insulator deposition process may improve field-effect mobility to more closely rival quaternary indium-containing ALD TFTs. [60] Prior work, using different deposition techniques or semiconductor oxides, has shown that activelayer thickness must be optimized to obtain good TFT stability [61] and enhancement mode behavior. [62] To investigate the effect of ZTO layer thickness on TFT behavior, three identical devices were fabricated using 5, 9, and 13 nm ZTO films deposited using the thermal ALD process at 200 ºC with post-deposition annealing at 500 ºC.…”

Solution processed ZnO homogeneous quasisuperlattice materials

“…With each additional periodic layer to the QSL, the top surface remains essentially identical, as a clean well-defined interface. A higher O vacancy content promotes n-type character as donors but also provides exceptional ambient air (moisture, O-containing air) stability for channel materials, as discussed by Liu et al 53 The surface electronic structure from Zn 2p and O 1s core-level photoemission is consistent and independent of QSL thickness. There is, however, a very slight shift in the binding energy of the Zn 2p spectra for a 1 L film.…”

Effects of Channel Thickness on Electrical Performance and Stability of High-Performance InSnO Thin-Film Transistors

“…Consequently, the V on negatively shifts with increasing t ITO and the µ FE increases with t ITO increasing from 6 to 9 nm. However, similar to other impurity dopants, more oxygen defects can induce more ionized impurity scattering, which possibly results in the degradation of µ FE with t ITO increasing from 9 to 15 nm [24]. 529.7 eV and O2 peak at around 531.3 eV, which can be regarded as metal-oxygen lattice and oxygen defects (oxygen vacancies and chemisorbed oxygen element), respectively [21].…”

“…Consequently, the Von negatively shifts with increasing tITO and the µFE increases with tITO increasing from 6 to 9 nm. However, similar to other impurity dopants, more oxygen defects can induce more ionized impurity scattering, which possibly results in the degradation of µFE with tITO increasing from 9 to 15 nm [24]. Drain current-drain voltage (ID-VD) curves of the ITO TFTs are measured, as shown in Figure 7a-d.…”