A Hybrid Gate Dielectrics of Ion Gel with Ultra-Thin Passivation Layer for High-Performance Transistors Based on Two-Dimensional Semiconductor Channels

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.

In-Plane Amorphous Oxide Ionotronic Devices and Circuits with Photochemically Enabled Favorable Interfaces

“…In this case, interestingly, the nearly selective deposition onto electrodes was achieved possibly due to dangling-bond-free surface of 2D materials. 42 Also, a polymeric thin film was employed for the elimination of direct contact between the ionic dielectric and S/D electrodes. Two hundred nanometers of the passivation layer was patterned by an ebeam lithography process.…”

“…However, there have been inherent limitations of the IL-dielectrics for practical applications mainly because of their fluidic property and undesirable parasitic capacitance (ionic conduction) in between the compositional electrodes of logic devices. The ionotronic devices typically suffer from long-term stability and large leakage current between electrodes due to the high fluidity of inherent liquidus properties and high ionic conductivity and unexpected impurities contamination of the IL-dielectric, respectively. − To overcome the fluidity, various ion gel (IG) formations, which secure locally confined mobile ions within a cross-linked polymer matrix have been successfully reported, exhibiting long-term stable and gel-like less fluidic properties even on flexible substrates. ,, Moreover, in recent years, significant efforts have been developed to minimize the parasitic capacitance of the devices. For instance, an ultrathin Al 2 O 3 film was deposited as a passivation layer by using an atomic layer deposition (ALD) system.…”

“…For instance, an ultrathin Al 2 O 3 film was deposited as a passivation layer by using an atomic layer deposition (ALD) system. In this case, interestingly, the nearly selective deposition onto electrodes was achieved possibly due to dangling-bond-free surface of 2D materials . Also, a polymeric thin film was employed for the elimination of direct contact between the ionic dielectric and S/D electrodes.…”

Reversible tuning of superconductivity in ion-gated niobium nitride ultrathin films by self-encapsulation with a high-$κ$ dielectric layer

“…Another possibility is to employ encapsulation techniques widely used to protect unstable or reactive 2D materials in standard solid-state FETs [71]. For example, one can cover the surface of the active materials, prior to the exposition to the electrolyte, with a high-quality ultrathin layered insulator obtained by micro-mechanical exfoliation of a bulk crystal [13,14,24], or a protective dielectric layer [39,72]. These alternatives, however, can present drawbacks when used in a ionic-gating setup.…”

“…For instance, the first approach is not easily scalable to multiple integrated devices and large-area geometries [13,14,24]. In the second approach, the thickness of the protective layer is critical: thick passivation films strongly suppress the gate capacitance [39,72], while thin uniform films cannot be deposited on several materials of interest [72]. The development of an alternative, complementary encapsulation technique is therefore highly desirable.…”