Gate Capacitance‐Dependent Field‐Effect Mobility in Solution‐Processed Oxide Semiconductor Thin‐Film Transistors

Abstract

4689www.MaterialsViews.com wileyonlinelibrary.com key in switching components for next generation displays such as smart windows, transparent mobile displays, and electronic papers. [1][2][3][4][5][6][7][8][9] Recently, high-quality OS fi lms on plastic substrates have been successfully fabricated by developing lowtemperature and solution-based processes (e.g., combustion process, [ 3 ] 'sol-gel on chip' process, [ 4 ] and photochemical activation methods [ 5 ] ). These methods can accelerate the adoption of fl exible OS TFTs to practical applications.While the novel OS fi lm-fabricating techniques are important, raising drive currents in low-operating voltages is also critical for low-power consuming and high-performance OS TFTs. [10][11][12][13] One of the conventional strategies to increase the drain current ( I D ) for transistors is to increase the gate-insulator capacitances ( C i ) based on the relationship of I D ∝ C i from the metal-oxide-semiconductor fi eldeffect transistors (MOSFETs) theory. [ 14 ] Empirically, such strategies has been applied to solution-processed OS TFTs. However, the enhanced behaviors of I D in the OS TFTs are quite different to that in MOSFETs, [ 3,5,[10][11][12][13] since disordered metal ions or dense grain boundaries in the solution-processed OSs make the fi eld-effect mobility ( μ FE ) of the OS TFTs depend on the total number of accumulated charge carriers in the channel. [ 15,16 ] Therfore, μ FE depends on C i , and I D is not in a linear relationship to C i . The relationship between C i and μ FE is important for low-voltage and high-performance solutionprocessed OS TFTs. Futhermore, theoretical predictions for the device performances can be essential guidelines for designing and optimizing integrated TFT circuits.The solution-processed OS disordering states can be categorized with nanocrystalline and amorphous states, which is determined by the number of metal elements that compose the OS fi lms. Binary oxide systems (number of metal elements = 1) such as ZnO, InO 2 , and SnO 2 , have nanocrystalline states, [ 6,7,12,13 ] while the ternary or quaternary oxide systems (number of metal elements > 1) like ZnSnO, InZnO, and InGaZnO have the amorhpous phases. [ 3,5,8 ] In the experiment, both nanocrystalline and amorhpous OS TFTs by engineering C i differ in electron-transporting mechanisms, but follow two Solution-processed oxide semiconductors (OSs) used as channel layer have been presented as a solution to the demand for fl exible, cheap, and transparent thin-fi lm transistors (TFTs). In order to produce high-performance and longsustainable portable devices with the solution-processed OS TFTs, the lowoperational voltage driving current is a key issue. Experimentally, increasing the gate-insulator capacitances by high-k dielectrics in the OS TFTs has signifi cantly improved the fi eld-effect mobility of the OS TFTs. But, methodical examinations of how the fi eld-effect mobility depends on gate capacitance have not been presented yet. Here, a systematic analysis of the fi eld...

Spray-combustion synthesis: Efficient solution route to high-performance oxide transistors

“…2 and SI Appendix, Fig. S13) (38). From these results, the SCS performance enhancement vs. spin-CS processing plausibly reflects more extensive M-O-M lattice densification and distortional relaxation, thereby reducing trap sites.…”

Use of high-k encapsulation to improve mobility in trap-limited metal-oxide semiconductors

“…Although this effect is very reliably reproduced experimentally , its precise cause is only beginning to be understood. This lack of understanding has led to recent attempts to identify a physical origin .…”

Fully Solution‐Processed Low‐Voltage Driven Transparent Oxide Thin Film Transistors

“…The increase of gate capacitance with high k dielectric may lower the activation energy of electron transition and lead to the filling of the tail state up to higher energy levels. Thus, the electron can easily jump to the transport bands in the percolation path, as demonstrated by the noticeably high mobility in our ZnO TFTs.…”

“…Materials with high k and good film forming ability are needed to increase the area normalized gate capacitance and to reduce the leakage current density. Numerous transparent and high k metal oxide dielectrics, such as AlO x , HfO 2 , ZrO x , AlO x , Y 2 O 3 , HfLaO x , and A1 2x‐1 Ti x O y , have been implemented into ZnO TFTs by solution processes. All of them could achieve excellent electron transport characteristics with mobility in a range of 0.18–45.5 cm 2 V −1 s −1 under an operating voltage of <10 V. Table shows a comparison of the results reported by ZnO TFTs with solution‐processed high k oxide dielectric.…”