Organic Thin Film Transistor Work Function Modification
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Solution Overview
Problem
Organic thin film transistors face challenges with lower charge mobilities, higher operating voltages, and increased hysteresis due to the formation of Schottky barriers between metal oxide source/drain electrodes and organic semiconductor layers, particularly when using metal oxide electrodes, which limits their performance in devices like display devices.
Innovation Solution
Treating the surface of metal oxide source/drain electrodes with a live ion-containing self-assembled monolayer (SAM) compound to increase the work function of the metal oxide relative to the organic semiconductor material, thereby enhancing charge mobility and reducing hysteresis by improving ion supply control as a function of applied electric charge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If metal oxide source/drain electrodes are used in organic thin film transistors, then the fabrication process is simplified and manufacturing cost is reduced, but Schottky barriers form at the interface with organic semiconductor layers, causing lower charge mobility and higher operating voltages
Solution Approach 1:
A self-assembled monolayer (SAM) is introduced as an intermediary layer between the metal oxide source/drain electrodes and the organic semiconductor layer. The SAM modifies the interface properties by adjusting the work function of the metal oxide, preventing Schottky barrier formation and enabling efficient charge injection. This mediator resolves the contradiction by maintaining the ease of manufacturing metal oxide electrodes while eliminating the performance degradation caused by direct contact with the organic semiconductor.
Solution Approach 2:
The work function of the metal oxide source/drain electrodes is changed by treating the surface with a self-assembled monolayer. This parameter change modifies the energy level alignment at the interface between the metal oxide and organic semiconductor, transforming the Schottky barrier into an ohmic contact. The parameter modification enables high charge mobility while retaining the manufacturing advantages of metal oxide electrodes.
2Device complexity
If the organic semiconductor layer is deposited directly on metal oxide source/drain electrodes, then the device structure is simplified, but Schottky barriers increase operating voltages to exceed 100 V and threshold voltages to be at least 50 times higher than silicon thin film transistors
Solution Approach 1:
The self-assembled monolayer serves as a mediator that modifies the electrical properties at the metal oxide-organic semiconductor interface. By adjusting the work function through SAM treatment, the interface enables low-voltage operation, reducing operating voltages from over 100 V to practical levels compatible with standard electronic circuits, while maintaining the simplified device structure.
3Reliability
If conventional SAM compounds containing thiol functional groups are used to treat metal oxide source/drain electrodes, then charge mobility may be improved, but these compounds bind only to metal surfaces like gold and not to metal oxide surfaces such as ITO
Solution Approach 1:
The chemical composition of the SAM compound is changed from thiol-functionalized compounds (which bind to metals) to compounds with functional groups that specifically bind to metal oxide surfaces. This parameter change in the chemical structure enables the SAM to adhere to metal oxide source/drain electrodes like ITO, maintaining the benefits of work function modification while ensuring compatibility with the metal oxide substrate.
Solution Approach 2:
A composite interface structure is created by combining the metal oxide source/drain electrode with a self-assembled monolayer that has specific affinity for metal oxide surfaces. This composite structure integrates the advantages of both materials: the electrical properties of metal oxide and the surface modification capabilities of the SAM, achieving both broad surface compatibility and improved charge mobility.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method increases charge mobility and decreases hysteresis in organic thin film transistors, making them suitable for applications in display devices by improving the interface properties between the insulating and semiconductor layers.
Implementation Method 1
the surfaces of the metal oxide source/drain electrodes are treated with a self-assembled monolayer (SAM) compound containing a live ion
Implementation Method 2
the surfaces of the metal oxide source/drain electrodes are treated with a self-assembled monolayer (SAM) compound
Implementation Method 3
decreasing hysteresis by improving ion supply control as a function of applied electric charge
Data Source
AI summary
Disclosed are methods of fabricating organic thin film transistors composed of a substrate, a gate electrode, a gate insulating film, metal oxide source/drain electrodes, and an organic semiconductor layer. The methods include applying a sufficient quantity of a self-assembled monolayer compound containing a live ion to the surfaces of the metal oxide electrodes to form a self-assembled monolayer. The presence of the live ion at the interface between the metal oxide electrodes and the organic semiconductor layer modifies the relative work function of these materials. Further, the presence of the self-assembled monolayer on the gate insulating film tends to reduce hysteresis. Accordingly, organic thin film transistors fabricated in accord with the example embodiments tend to exhibit improved charge mobility, improved gate insulating film properties and decreased hysteresis associated with the organic insulator.