Novel Tunnel‐Contact‐Controlled IGZO Thin‐Film Transistors with High Tolerance to Geometrical Variability

Abstract

Thin insulating layers are used to modulate a depletion region at the source of a thin‐film transistor. Bottom contact, staggered‐electrode indium gallium zinc oxide transistors with a 3 nm Al2O3 layer between the semiconductor and Ni source/drain contacts, show behaviors typical of source‐gated transistors (SGTs): low saturation voltage (VD_SAT ≈ 3 V), change in VD_SAT with a gate voltage of only 0.12 V V−1, and flat saturated output characteristics (small dependence of drain current on drain voltage). The transistors show high tolerance to geometry: the saturated current changes only 0.15× for 2–50 µm channels and 2× for 9‐45 µm source‐gate overlaps. A higher than expected (5×) increase in drain current for a 30 K change in temperature, similar to Schottky‐contact SGTs, underlines a more complex device operation than previously theorized. Optimization for increasing intrinsic gain and reducing temperature effects is discussed. These devices complete the portfolio of contact‐controlled transistors, comprising devices with Schottky contacts, bulk barrier, or heterojunctions, and now, tunneling insulating layers. The findings should also apply to nanowire transistors, leading to new low‐power, robust design approaches as large‐scale fabrication techniques with sub‐nanometer control mature.

Crystallized Monolayer Semiconductor for Ohmic Contact Resistance, High Intrinsic Gain, and High Current Density

“…Even the output curves of the device having the longest channel (50 µm as channel length) still show a clear contact-limited behavior ( Figure S3e, Supporting Information). [24,25] The drain-source current (I D ) is restricted by the poor injection from the source electrodes and independent of the channel resistance. This is further confirmed by the cross-sectional transmission electron microscopy (TEM) image in Figure 1b, where the evaporated Au would penetrate the organic layer and contact with the SiO 2 substrate directly even at a low deposition speed of 0.2 Å s −1 .…”

“…The intrinsic gain (A v ) defines the maximum voltage gain that a single OFET can achieve, and it is an important figure of merit for OFETs working in saturation regime. [24,25,46] From the definition of A v = g m /g d , the essential properties to achieve a high A v are high transconductance (g m = ∂I D /∂V G ) and low output conductance (g d = ∂I D /∂V DS ). To fulfill the demands in high density and high speed for future organic electronics, short-channel OFETs with high A v values are necessary.…”

“…Second, due to the reverse bias nature, the capacitive effect at contact can also be induced by the formation of depletion region under the source contact. [24,25] However, this depletion effect would disappear once the bias is removed. The relatively long recovery time in our device suggests the depletion effect should be a less important reason for the current saturation in the short-channel 1L-OFETs.…”

Compact Source-Gated Transistor Analog Circuits for Ubiquitous Sensors

“…1a and 1b show cross-sections of two SGTs with sourcegate overlap S and source-drain separation, d. (SGTs ordinarily do not use the more general notation L for sourcedrain gap, as their effective channel length varies with applied bias in a manner additional to channel length shortening in FETs, hence the distinct terminology). SGTs have been explored in a variety of materials including amorphous [29] and polysilicon [23], [25], [28], [30], ZnO [31], InGaZnO (IGZO) [26], [32], organics [33], MoS2 [34] and semimetals [26], with several means of engineering an energy barrier at the source, including Schottky contacts ( Fig. 1a), bulk unipolar contacts [35], [36], or incorporating a tunnel barrier [32] (Fig.…”

31‐1: Invited Paper: The Multimodal Thin‐Film Transistor (MMT): A Versatile Low‐Power and High‐Gain Device with Inherent Linear Response

“…Building on our activities in bespoke TFT designs [4][5][6][7], we introduce a new transistor concept which offers numerous application benefits while being fully compatible with current fabrication processes. The new structure, called the Multimodal Transistor (MMT) ( Fig.…”