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Scalable, Low Voltage Device For Liquid Crystal-Based Technologies

A multi-stable liquid crystal (LC) device based on saddle-spray director variation that enables fast optoelectronic switching and has low power requirements.

Problem:

LC devices are crucial for a number of modern technologies including monitors, electronic switches, and storage devices. These devices rely on an optoelectrical process by which applied current induces changes in the intrinsic molecular orientation of an LC. However, currently available devices are limited by complex fabrication processes, high threshold voltage requirements and slow switching speeds.

Solution:

The current invention addresses this problem by providing a fast, multi-stable LC device with low threshold voltage requirements, showing a threshold switching electric field of 0.5V/mm. The device consists of annular ring-based arrays plated on copper electrodes which are easily manipulated by applying current across the device. Unique to this invention is the utilization of saddle-splay effects, which are routinely suppressed in other LC systems. Therefore, generic, achiral liquid crystals exhibit spontaneously broken surface symmetries, leading to emergence of chiral and polar arrangements that can couple to directional DC fields and be extended across the domains. Thus, this technology opens new avenues for the development of more advanced, higher efficiency LC based technologies.

Technology:

The technology takes advantage of “saddle-splay” elasticity in LCs. Using combinations of lithographic patterning and selective surface functionalization, surface patterns are created with spatially defined geometry and precisely controlled surface chemistry. Broken symmetry regimes are defined, and the desired patterning geometry results in a multi-state stable LC display device that can be switched at an extremely low voltage density.

Advantages:

The threshold switching electric field of 0.5V/mm demonstrates the low switching field
Has a low threshold voltage resulting in low power requirements
The fabrication process is simple and easily scalable, and compatible with the conventional photolithography process
Saddle-splay technology enables switching between eight states compared to just four with traditional LC systems

Demonstration of a multistable LC switching device from a patterned square array of annuli. a) Schematic of the device setup with top and bottom copper electrodes patterned on glass slides. b—e) A set of stable, cardinal states that can be switched upon the application of a small (0.5 V/μm) transverse, directional electric field as indicated by the yellow arrow. Each of these states remains stable upon removal of the field and any starting state can be used as a precursor to any chosen new state. f) By careful tuning of the applied field, the system can also access the four ordinal states, in which the defects reside along system diagonals (total of eight states vs. four from the conventional LC devices). All scale bars are 20 μm. Insets show the simulation configuration, with the distorted regions highlighted.