Frequency-Stable Ionic-Type Hybrid Gate Dielectrics for High Mobility Solution-Processed Metal-Oxide Thin-Film Transistors

Abstract

In this paper, we demonstrate high mobility solution-processed metal-oxide thin-film transistors (TFTs) by using a high-frequency-stable ionic-type hybrid gate dielectric (HGD). The HGD gate dielectric, a blend of sol-gel aluminum oxide (AlOx) and poly(4-vinylphenol) (PVP), exhibited high dielectric constant (ε~8.15) and high-frequency-stable characteristics (1 MHz). Using the ionic-type HGD as a gate dielectric layer, an minimal electron-double-layer (EDL) can be formed at the gate dielectric/InOx interface, enhancing the field-effect mobility of the TFTs. Particularly, using the ionic-type HGD gate dielectrics annealed at 350 °C, InOx TFTs having an average field-effect mobility of 16.1 cm2/Vs were achieved (maximum mobility of 24 cm2/Vs). Furthermore, the ionic-type HGD gate dielectrics can be processed at a low temperature of 150 °C, which may enable their applications in low-thermal-budget plastic and elastomeric substrates. In addition, we systematically studied the operational stability of the InOx TFTs using the HGD gate dielectric, and it was observed that the HGD gate dielectric effectively suppressed the negative threshold voltage shift during the negative-illumination-bias stress possibly owing to the recombination of hole carriers injected in the gate dielectric with the negatively charged ionic species in the HGD gate dielectric.

Understanding, Optimizing, and Utilizing Nonideal Transistors Based on Organic or Organic Hybrid Semiconductors

“…The EDL capacitor is formed by electrostatic accumulation, whereas the pseudo‐capacitor is formed by the Faradaic charge‐transfer process, which is an electrochemical process (Figure d) . With these materials as capacitors, the C ‐ f diagram can be displayed in three cases (Figure e): 1) a normal dielectric only containing bulk capacitance (bottom); 2) an electrolyte‐like dielectric containing EDL capacitance and bulk capacitance (middle); 3) an electrolyte‐like dielectric layer containing pseudocapacitance, EDL capacitance and bulk capacitance (top) . In particular, oxide materials (e.g., SiO x and AlO x ) fabricated by the solution method can be called ionic conductors or solid‐state electrolytes, which is defined as a solid material conducting mainly by ionic migration but acting as an insulator for electrons .…”

Solution-processed amorphous gallium-tin oxide thin film for low-voltage, high-performance transistors

“…It is acknowledged that electrical double layer formed in the solution-processed metal oxide gate dielectrics will lead to higher capacitance [41,42], as shown in the inset of Fig. 6b.…”

Evidence for Pseudocapacitance and Faradaic Charge Transfer in High-Mobility Thin-Film Transistors with Solution-Processed Oxide Dielectrics

“…13 Heo et al attributed the mobility enhancement to electric double layer (EDL) formation at the solutionprocessed AlO x /InO x interface. 14 In most cases, large capacitance induced by EDL can lead to low operating voltage. However, numerical simulations have revealed that, once the…”

“…The strong dependence of capacitance on frequency and voltage suggests the possible formation of pseudocapacitance in addition to the EDL. 19 Usually, solution-processed gate dielectrics fabricated at low temperatures are not dense and feature unintentional defects causing cations and anions, 14 which can be regarded as solid-state electrolytes. 20−22 With the EDL effect, charge accumulation is achieved electrostatically at the gate/electrolyte and electrolyte/semiconductor interfaces, and the EDL capacitance C EDL arises from the surface-charge density.…”

“…However, for some TFTs with high- k gate dielectrics, the mobility was not enhanced. , Zeumault et al proposed that donor-like traps in ZrO 2 are aligned at shallow energies with respect to the transport band of ZnO and provide more carriers in the ZnO channel by charge migration at the insulator/semiconductor interface, resulting in high mobility . Heo et al attributed the mobility enhancement to electric double layer (EDL) formation at the solution-processed AlO x /InO x interface . In most cases, large capacitance induced by EDL can lead to low operating voltage.…”