Instability in threshold voltage and subthreshold behavior in Hf–In–Zn–O thin film transistors induced by bias-and light-stress

Abstract

Electrical bias and light stressing followed by natural recovery of amorphous hafnium-indium-zinc-oxide (HIZO) thin film transistors with a silicon oxide/nitride dielectric stack reveals defect density changes, charge trapping and persistent photoconductivity (PPC). In the absence of light, the polarity of bias stress controls the magnitude and direction of the threshold voltage shift (ΔVT), while under light stress, VT consistently shifts negatively. In all cases, there was no significant change in field-effect mobility. Light stress gives rise to a PPC with wavelength-dependent recovery on time scale of days. We observe that the PPC becomes more pronounced at shorter wavelengths.

Reduction of the interfacial trap density of indium-oxide thin film transistors by incorporation of hafnium and annealing process

“…[20][21][22][31][32][33][34] Chong et al reported that amorphous Hf-InZnO TFTs exhibited a small positive V th shift of about 1.8 V after BS for 60 h. However, even though there are positive reports on the high stability of OxTFTs, an issue originating from Zn has also been reported. Liu et al reported that hydrogen ions dissociate from the ZnO-H bonds in InGaZnO TFTs, resulting in an instability under BS.…”

“…In the above results, group IV elements (such as Ti, Zr, Sn and Hf) play an important role in suppressing the excess charge carrier generation and improving the stability of the TFTs by binding with oxygen. [18][19][20][21][22][23][24][25] For InZnO incorporated with Si, a 3.7 V shift in the threshold voltage (V th ) after 6.5 h was reported. 23 Because of the lower interfacial trap density, the Zr-InZnO TFTs annealed at 350…”

“…Using the concept of a vacancy suppressor in amorphous films, further intentional doping of the base oxide with metals has been demonstrated. Some examples include InZnO doped with Sn (Sn-InZnO), 18,19 Hf-InZnO, [20][21][22] Si-InZnO, 23 Zr-InZnO 24 and Ti-InZnO. 25 Although this doping method has achieved high stabilities, extra dopant needs to be incorporated to stabilize the film properties because of the instability of the films that contain Zn.…”

“…Thin film transistors based on amorphous oxide films (OxTFTs) have attracted tremendous interest as TFT backplanes in active-matrix organic light emitting diodes (OLEDs) and liquid crystal displays owing to their high mobilities. [1][2][3][4][5][6][7] Intensive developments on oxide compounds including InO x -based, [8][9][10][11][12][13] ZnO x -based, 14 SnO x -based 15 and mixed channel materials such as InZnO x -based OxTFTs [16][17][18][19][20][21][22][23][24][25] have been widely studied in OxTFTs in recent decades because of their excellent electrical stabilities and high mobilities. Among them, InGaZnO (IGZO) 1,2,26 and InSnZnO (ITZO) 18,19 are currently being developed for use as commercial TFT backplanes because of their superior properties and high electron mobilities.…”

Effects of dopants in InOx-based amorphous oxide semiconductors for thin-film transistor applications

“…In terms of bond strength to oxygen atoms, Hf doping is also expected to have similar effects to Si doping. [31][32][33] However, to clarify the carrier transport in the present InO xbased semiconductors based on thermal activation, energy band diagrams, and local atomic structure, we will discuss further characterization, such as low temperature I-V measurements, 34 Hall measurements, 35,36 and X-ray absorption spectroscopy, 13,37 in another report. In conclusion, we fabricated amorphous oxide TFTs based on InO x semiconductors doped with Ti, W, or Si atoms.…”