High performance, 2D materials device fabrication for flexible electronics

Stanford researchers have developed a high performance, 2D material, staggered top-gate architecture, embedded contact, flexible electronic device. Previous 2D material device performance has been limited by coplanar architecture, and/or degradation from process residue. This invention addresses past design and fabrication challenges: the 2D material is grown via Chemical Vapor Deposition on a rigid substrate, and then contacts are deposited and patterned before the entire stack is transferred using DI water to a flexible substrate. (Figure 1.)

Embedding the contacts and directly coating the flexible substrate on top minimizes damage of the 2D material during the transfer process. The 2D material can also be passivated immediately after the transfer, further minimizing surface contamination. The top surface of the released flexible substrate is perfectly flat as is the 2D material/growth substrate's interface, and all previously patterned 3D layers are embedded within the polymer substrate. The planar device topography is optimal for ultrathin device stacks consisting only of a few atoms (e.g., vertical RRAM). Advanced lithography techniques can be used to pattern transistors with small channel lengths down to 50 nm on the planar, rigid substrate. This method makes it possible to fabricate high performance, field-effect transistors in staggered top-gate architecture with gated contact areas.

Stage of Development – Proof of Concept
Researchers in the Pop lab at Stanford have fabricated top-gate staggered MoS₂ FET prototypes down to 50 nm channel length, and flexible RRAM. Flexible FETs with CVD-grown MoS₂ on 6 µm thick polyimide have achieved:

Field-effect mobility up to ? 53 cm²V^-1s^-1
I_D,on ? 630 µA/µm

The Pop lab is working on first circuits using the technology, and radiofrequency operation optimization by introducing further fabrication/patterning steps before the transfer. Future plans include sensors and optoelectronics devices.