Abstract
We propose a hybrid gate structure for ion gel dielectrics using an ultra-thin Al2O3 passivation layer for realizing high-performance devices based on electric-double-layer capacitors. Electric-double-layer transistors can be applied to practical devices with flexibility and transparency as well as research on the fundamental physical properties of channel materials; however, they suffer from inherent unwanted leakage currents between electrodes, especially for channel materials with low off-currents. Therefore, the Al2O3 passivation layer was introduced between the metal electrodes and ion gel film as a leakage current barrier; this simple approach effectively reduced the leakage current without capacitance degradation. In addition, we confirmed that a monolayer MoS2 transistor fabricated with the proposed hybrid gate dielectric exhibited remarkably enhanced device properties compared to a transistor using a normal ion gel gate dielectric. Our findings on a simple method to improve the leakage current properties of ion gels could be applied extensively to realize high-performance electric-double-layer transistors utilizing various channel materials.
Highlights
IntroductionIonic liquids provide the advantage of very large capacitances by the formation of nanogap capacitors at solid– liquid interfaces[1,2], and electric double-layer-transistors (EDLTs) using ionic liquids have received significant attention because they show ultra-high capacitance and potential applicability in both practical flexible and transparent devices and studies on the fundamental physical properties of channel materials, including carrier transport phenomena, superconductivity, and thermoelectricity[3,4,5,6,7,8,9,10,11,12,13]
We propose a hybrid gate dielectric structure composed of an ion-gel film and ultra-thin Al2O3 passivation layer deposited by atomic layer deposition (ALD) to improve the electrical properties of the ion-gel-based 2D transistor, because Al2O3 films exhibit good leakage current properties and the ultra-thin Al2O3 layer can act as a leakage current barrier without causing significant capacitance drops[38,39,40]
The ion gel films were prepared from a solution of the triblock copolymer poly(styrene-block-methyl methacrylate-block-styrene) (PS-poly(methyl methacrylate) (PMMA)-PS) and the ionic liquid 1-ethyl-3-methylimi dazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]), in ethyl propionate as an organic solvent
Summary
Ionic liquids provide the advantage of very large capacitances by the formation of nanogap capacitors at solid– liquid interfaces[1,2], and electric double-layer-transistors (EDLTs) using ionic liquids have received significant attention because they show ultra-high capacitance and potential applicability in both practical flexible and transparent devices and studies on the fundamental physical properties of channel materials, including carrier transport phenomena, superconductivity, and thermoelectricity[3,4,5,6,7,8,9,10,11,12,13]. The optimized dielectric structure was applied to a monolayer MoS2 transistor and compared to a transistor using a normal ion-gel gate dielectric to confirm the effect of the proposed hybrid dielectrics on the transistor performance
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