“…Several studies have been directed toward improving device stability through the incorporation of various metal cations such as Ga, Zr, Y, and Hf. [53][54][55][56][57][58] These metal cations form stronger bonds with oxygen than does Zn, and the addition of such metal cations can suppress oxygen vacancy formation to reduce charge carrier generation in ZnO films, which in turn improves the device stability.…”
“…Several studies have been directed toward improving device stability through the incorporation of various metal cations such as Ga, Zr, Y, and Hf. [53][54][55][56][57][58] These metal cations form stronger bonds with oxygen than does Zn, and the addition of such metal cations can suppress oxygen vacancy formation to reduce charge carrier generation in ZnO films, which in turn improves the device stability.…”
“…15 Device stability can be improved by the incorporation of metal cations which have a higher ionic valence and stronger oxygen affinity than Zn 2+ such as Ga 3+ , Y 3+ , Sc 3+ , and La 3+ in group III and Hf 4+ , Sn 4+ , and Si 4+ in group IV. [16][17][18][19][20][21] The addition of these metal cations suppresses oxygen vacancy formation, which reduces the charge carrier concentration and, in turn, improves the device stability. To incorporate such a carrier suppressor into an aqueous ammine-hydroxo Zn solution, the corresponding metal hydroxides should be soluble in ammonium hydroxide.…”
Highly stable and high performance solution-processed amorphous oxide semiconductor thin film transistors (TFTs) were produced using a Li and Zr co-doped ZnO-based aqueous solution. Li and Zr co-doping at the appropriate amounts enhanced the oxide film quality in terms of enhanced oxygen bonding and reduced defect sites. The 0.5 mol% Li and 1.0 mol% Zr co-doped ZnO TFTs annealed at 320 C exhibited noticeably lower threshold voltage shifts of 3.54 V under positive bias stress and À2.07 V under negative bias temperature stress than the non-doped ZnO TFTs. The transistors revealed a good device mobility performance of 5.39 cm 2 V À1 s À1 and an on/off current ratio of 10 8 when annealed at 320 C, compared to a mobility performance of 2.86 cm 2 V À1 s À1 and an on/off current ratio of $10 7 when annealed at 270 C. Our results suggest that Li and Zr co-doping can be a useful technique to produce more reliable and low temperature solution-processed oxide semiconductor TFTs.
“…The field-effect mobility is affected by shallow traps near the conduction band and the interaction of oxygen vacancies, and zinc interstitials is an important source of n-type conductivity in ZnO [25, 26]. Therefore, suppressing the generation of oxygen-vacancy-related defects with Hf doping can effectively decrease the mobility [25]. Decrease in the SS value of HZO-TFT indicates a reduction in interface trap density.Fig.…”
Thin-film transistors (TFTs) with atomic layer deposition (ALD) HfZnO (HZO) as channel layer and Al2O3 as gate insulator were successfully fabricated. Compared with ZnO-TFT, the stability of HZO-TFT was obviously improved as Hf doping can suppress the generation of oxygen related defects. The transfer characteristics of TFTs at different temperatures were also investigated, and temperature stability enhancement was observed for the TFT with Hf doping. The density of states (DOS) was calculated based on the experimentally obtained E
a, which can explain the experimental observation. A high-field effect mobility of 9.4 cm2/Vs, a suitable turn-on voltage of 0.26 V, a high on/off ratio of over 107 and a steep sub-threshold swing of 0.3 V/decade were obtained in HZO-TFT. The results showed that temperature stability enhancement in HfZnO thin-film transistors are attributed to the smaller DOS.
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