Material New Technology Presentation Meetings
High quality IGZO transistor is formed by 150 ℃ low temperature process

October 30, 2018, “Material New Technology Presentation Meetings” was held in JST. In this here, an oral presentation by Dr. Furuta of Kochi University of Technology is picked up.

Figure 1. Characterics of IGZO diode1)

As presentation title, the research group tried to manufacture IZGO (In-Ga-Zn-O) transistor by making use of low temperature process, in order to correspond to flexible devices. As you know, maximum process temperature is 300 - 400 ℃ in the annealing process after IGZO film deposition, in the present moment. For this reason, glass or high thermal resistance plastic film for example polyimide film should be used as a substrate. In this research, maximum process temperature was lowered to 150 ℃ due to using PEN film, is relatively inexpensive.

IGZO film was deposited by the conventional sputtering method. However, a certain gas was purged into the process chamber with O2 gas (flow rate 1 %) due to low annealing process. This is reason why oxygen defect which is a typical defect in oxide semiconductor is suppressed. In fact, if this gas was doped at 8 % ratio , carrier density was reduced from 1.8×10¹⁸cm^-3 to 7.2×10¹⁶cm^-3. As a result, annealing temperature can be lowered to 150 ℃.

Figure 1 shows transfer characteristics of sample device, was manufactured by this low temperature process (150 ℃). It was almost same as that of the conventional device with glass substrate. Table 1 shows comparison of device catachrestic. While they are compared, carrier mobility and hysteresis of new device were mere low, however, subthreshold characteristic was superior. In short, if 150 ℃ low temperature process is adopted, high quality oxide transistor can be manufactured, and then, PEN film can be used as a substrate.

Carrier mobility (cm2/Vs) Subthreshold (V/dec.)  Hysteresis (V) Conventional (300℃) 14.5 0.4  0.5 New (150℃) 13.4 0.1  0.6

Table 1. Comparison of transistor characteristics1)

Abstract is the above. However, not only kind of doped gas and its purged method but also reduction mechanism of defect in this process were not disclosed. Therefore, its content was seemed to be insufficient for audience inclusive of author.

Reference
1)Furuta：A New Low Temperature Forming Technology in High Quality Oxide-Semiconductor Manufacturing Process for Flexible Device, Material New Technology Presentation Meetings!, pp.3-6 (2018.10)

※This title is translated arbitrarily by Stella News Site because of without English edition of presentation material.