N-Type 2D TMD Transistor With BEOL-Compatible Ohmic Contacts
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Solution Overview
Problem
Existing microelectronics based on silicon and silicon germanium face challenges in integrating 2D transition metal dichalcogenide (TMD) transistors due to incompatibility with Back End Of Line (BEOL) processing temperatures and requirements for TMD doping and source/drain-to-TMD contact resistance, limiting their integration with non-TMD semiconductor materials.
Innovation Solution
A method for fabricating TMD transistors involving a substrate with an insulating layer, an n-type 2D TMD layer doped with aluminum, metal source and drain electrodes with low resistance ohmic contacts, and a gate dielectric structure that supports capacitive coupling and low leakage, all within a thermal budget compatible with BEOL processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If TMD transistors are integrated with silicon and silicon germanium microelectronics, then device functionality and circuit performance are improved, but compatibility with BEOL process temperature constraints is worsened due to high temperature processing requirements
Solution Approach 1:
The patent changes the temperature parameter by using low-temperature processing techniques (below 500°C) to fabricate TMD transistors, thereby adapting to the BEOL process temperature constraints while maintaining device functionality and enabling integration with silicon and silicon germanium microelectronics
Solution Approach 2:
The patent performs preliminary doping of the TMD channel layer with aluminum before transistor fabrication to achieve desired electrical characteristics early in the process, which allows subsequent low-temperature processing steps to proceed without requiring high-temperature annealing or re-doping, thus satisfying both performance and temperature constraint requirements
2Reliability
If aluminum doping is used to achieve n-type TMD channels, then carrier concentration and electrical performance are improved, but control over doping concentration and uniformity becomes more difficult
Solution Approach 1:
The patent performs preliminary doping of the TMD channel layer with aluminum atoms deposited in a thin layer (e.g., 1-10 nm) before transistor fabrication. This preliminary doping action allows precise control over the doping concentration by controlling the aluminum layer thickness, and ensures uniform doping throughout the channel layer, thereby achieving both improved electrical performance and manufacturing precision
Solution Approach 2:
The patent applies aluminum doping locally to the TMD channel layer region where it is needed, using techniques such as atomic layer deposition (ALD) or molecular beam epitaxy (MBE) to deposit aluminum atoms only in the channel area. This localized doping approach improves electrical performance in the active region while avoiding unnecessary doping in other areas, and allows precise control over the doping concentration and spatial distribution
3Productivity
If low resistance ohmic contacts are formed between metal electrodes and TMD, then current flow and device performance are improved, but contact resistance requirements become more stringent and difficult to satisfy
Solution Approach 1:
The patent performs preliminary doping of the TMD channel layer with aluminum atoms in the contact regions before metal electrode deposition. This preliminary doping creates highly doped n-type regions under the metal electrodes, which form low resistance ohmic contacts with the metal. By controlling the aluminum doping concentration and distribution in advance, the patent achieves the required low contact resistance without needing to impose extremely stringent control requirements during the metal deposition and annealing processes
Solution Approach 2:
The patent uses the aluminum-doped TMD layer as an intermediary between the metal electrode and the intrinsic TMD channel. The heavily doped aluminum region acts as a transition layer that facilitates charge carrier injection from the metal into the TMD channel, reducing the Schottky barrier height and forming a low resistance ohmic contact. This intermediary doping layer makes it easier to achieve low contact resistance by providing a gradual transition in doping concentration rather than requiring direct contact between metal and intrinsic TMD
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
Enables the integration of TMD transistors with silicon-based microelectronics by ensuring low resistance contacts and thermal compatibility, facilitating the formation of composite circuits with high on-state currents and low off-state currents.
Implementation Method 1
a un-doped 2D TMD layer is transformed into an n-type 2D TMD layer by doping with aluminum
Implementation Method 2
metal source and drain electrodes with low resistance ohmic contacts
Implementation Method 3
a gate dielectric structure that allows capacitive coupling
Data Source
AI summary
A transition metal dichalcogenide (TMD) transistor includes a substrate, an n-type two-dimensional (2D) TMD layer, a metal source electrode, a metal drain electrode, and a gate dielectric. The substrate has a top portion that is an insulating layer, and the n-type 2D TMD layer is on the insulating layer. The metal source electrode, the metal drain electrode, and the gate dielectric are on the n-type 2D TMD layer. The metal gate electrode is on top of the gate dielectric and is between the metal source electrode and the metal drain electrode.