Study On The Performances Of Cosputtered Al-Zn-Sn-O Thin Film Transistors

With the development of the next display gradually toward high resolution、large size and flexibility, it needs increasingly high demand for backplanetechnology. As the representative of the amorphous oxide thin film transistors,In-Ga-Zn-O (IGZO) thin film transistors have attracted the attention of peoplearound the world because of their merits such as high mobility, good transparency,good large-area uniformity, and so on. Moreover, the display panel depended on thebackplane technology of IGZO thin film transistors has the advantage of low powerconsumption. However, IGZO contains rare elements of In, Ga which is notconducive to reducing the cost. It is of great significance to study oxide thin filmtransistors whose performances can be in comparison with IGZO oxide thin filmtransistor but without rare elements.From the perspective of replacing rare elements, and according to the carriertransport mechanism of IGZO film, we use Al and Sn respectively to replace Ga andIn elements of IGZO films. Using magnetron sputtering process which is compatiblewith modern industrial production, we prepared Al-Sn-Zn-O (AZTO) film and AZTOthin film transistor by cosputtering with three targets Al2O3、ZnO and SnO2,respectively. Specific works are as follows:1、We prepared AZTO film with different Al2O3contents by adjusting the powerof Al2O3in sputter deposition process. The results indicated that all AZTO films wereamorphous and the AZTO film had high transmittance at different Al2O3depositionpower. The transmittance was above85%in550nm wavelengths which was sensitiveof human’s eye.2、We prepared AZTO thin film transistors with different Al2O3deposition power,and studied the performances of AZTO thin film transistors with different Al2O3deposition power. The results indicated that with the deposition power of Al2O3increasing, the mobility decreased and threshold voltage increased. But the transfer characteristics and Ion/Ioffof the devices were improved effectively. We believe thatthe Al in AZTO TFT acted as a role of suppressing carrier like Ga. Then, we obtaineda preferable performance of device, when deposition power of Al2O3was20W. Thecontents of Zn, Sn, Al and O in no annealing AZTO film were17%,3%,2%and78%individually, when deposition power of Al2O3was20W, measured by SEM(JSM-7500F).3、We prepared devices with different active layer thickness and studied theinfluence of the active layer thickness on the device performances. It was found thatthe thickness of the active layer greatly affected the performances of the device.When the thickness was too thin, the number of carriers was too low and the mobilitywas not high. And when the thickness was too thick, it would increase the carrierinjection resistance. In addition, the too thick thickness would also increase thenumber of carriers greatly which leaded to scatter effect. Both of them makedmobility declined. When the active layer thickness was45nm, we get the optimaldevice performances.4、Above to the best device obtained, we further studied the positive biasstability of the device. It was found that, under positive gate-bias stress, the thresholdvoltage of the device leaded to a positive shift. This was because that the free carrierswas attracted to the interface of the channel layer and the insulating layer by gatevoltage. And the free carriers were trapped by the negative charge traps in theinterface of the channel layer and the insulating layer, or were captured by the bulktraps of insulating layer when injected into the insulating layer. Therefore, the numberof carriers reduced, and the threshold voltage generated a positive shift.