We report ZnO TFTs using Al2O3/Ta2O5 bilayer gate dielectrics grown by atomic layer deposition. The saturation mobility of single layer Ta2O5 dielectric TFT was 0.1 cm(2) V(-1) s(-1), but increased to 13.3 cm(2) V(-1) s(-1) using Al2O3/Ta2O5 bilayer dielectric with significantly lower leakage current and hysteresis. We show that point defects present in ZnO film, particularly VZn, are the main reason for the poor TFT performance with single layer dielectric, although interfacial roughness scattering effects cannot be ruled out. Our approach combines the high dielectric constant of Ta2O5 and the excellent Al2O3/ZnO interface quality, resulting in improved device performance.

We report reproducible multibit transparent flash memory in which a single solution-derived TaO layer is used simultaneously as a charge-trapping layer and a tunneling layer. This is different from conventional flash memory cells where two different dielectric layers are typically used. Under optimized programming/erasing operations, the memory device shows excellent programmable memory characteristics with a maximum memory window of ∼10.7 V. Moreover, the flash memory device shows a stable 2-bit memory performance and good reliability, including data retention for more than 10 s and endurance performance for more than 100 cycles. The use of a common charge-trapping and tunneling layer can simplify the fabrication of advanced flash memories.

the channel stack is explained. Although there may be other methods to achieve the same outcome (e.g., ion implantation and capping layers), this is the first report that shows the multi layer channel approach can achieve decoupling of threshold voltage control from fieldeffect mobility enhancement.The fabricated devices include singlelayer ZnO channel TFTs and multilayer ZnO/HfO 2 channel TFTs. The total ZnO film thickness (in both single and multilayer channels) was varied from 90 to 160 cycles (13.5, 18, and 24 nm at ≈0.15 nm per cycle), but the HfO 2 oxide layers were fixed at 5 cycles (0.7 nm at ≈0.14 nm per cycle) each. We kept the total ZnO thickness in the single and multiple channel TFTs constant. For example, a 160 cycle ZnO film in single channel TFT configuration means that the channel was single layer ZnO film with 160 atomic layer deposition (ALD) cycles. In contrast, a 160 cycle ZnO film in multilayer TFT configuration means that the sum total of all individual ZnO layers in the multilayer channel is 160 cycles (excluding the HfO 2 layers). Schematics of the TFTs with single layer and multilayer channels are shown in Figure 1a,b. The total thickness of the ZnO in either TFT configuration was varied as 90, 120, or 160 cycles. Note that there is an additional HfO 2 layer in contact with the Indium tin oxide (ITO) gate in both TFT configurations (Figure 1a,b). This HfO 2 layer serves as the main gate insulator and is quite thick (140 nm). This is different from the thin layers (5 cycle, 0.7 nm, HfO 2 layers) embedded between the ZnO semiconductor layers, although both are deposited by the same ALD process.Transfer characteristics of the two TFT configurations, measured at a drain voltage of +10 V (saturation regime), are shown next to each schematic in Figure 1. In the case of single layer channel TFT, as shown in Figure 1a, decreasing the ZnO thickness from 160 to 90 cycles, resulted in a large V TH shift toward enhancement mode operation, which is a desirable result. However, we simultaneously observed a large drop in the drain current (I D , Figure 1a), which means that the field effect mobility has been degraded. However, when alternating ZnO/HfO 2 films were used as the channel layer, the transfer characteristics were markedly different, as shown in Figure 1b. The subthreshold swing (SS) values for these TFTs are shown in Figure S1 (Supporting Information). The extracted V TH of the multilayer channel TFTs shifted gradually from around −2.6 ± 0.2 to −2.1 ± 0.3 V, while the devices still showed deple tion mode (V TH < 0 V) operation. Interestingly, the I D remained constant for all multilayer TFTs, as shown in the zoomedin region of Figure 1b. Thus, it appears that multilayer channels allow us to independently control the threshold voltage without degrading the drain current. Figure 2a,b shows a summary of the performance of single layer and multilayer channel TFTs as a function of total ZnO thickness. The horizontal axes in Figure 2a,b show thicknessTransition metal oxide (TMO) semiconductors hav...

No abstract

The comparative utilization of solar thermal or photovoltaic systems has significantly increased to fulfill the requirement of electricity and heat since few decades. These hybrid systems produce both thermal and electrical energy simultaneously. In recent times, increasing interest is being redirected by researchers in exploiting variety of nanoparticles mixed with miscellaneous base fluids (hybrid nanofluid) for these hybrid systems. This new class of colloidal suspensions has many fascinating advantages as compared to conventional types of nanofluids because of their modified and superior rheological and thermophysical properties which makes them appealing for solar energy devices. Here, we have attempted to deliver an extensive overview of the synthetic methodologies of hybrid nanofluids and their potential in PV/T and solar thermal energy systems. A detailed comparison between conventional types of nanofluids and hybrid nanofluids has been carried out to present in-depth understanding of the advantages of the hybrid nanofluids. The documented reports reveal that enhanced thermal properties of hybrid nanofluids promise the increased performance of solar thermal PV/T systems. Additionally, the unique properties such as nanoparticles concentration and type of base fluid, etc. greatly influence the behavior of hybrid nanofluidic systems. Finally, the outlook, suggestions, and challenges for future research directions are discussed.