Flexible Memristor Chips

Engineers at the National Institute of Standards and Technology (NIST) have developed electronic memory chips that can be bent and twisted without fracture. These flexible chips are fabricated with readily available and relatively inexpensive materials. According to the scientists, not only do the chips have a prominent physical attribute, but they also appear to possess “memristor-like” characteristics. A memristor, short for ‘memory resistor’, has a fascinating characteristic due to which it can ‘remember’ the amount of charge that has flowed through it.
 The chip, which possesses memristor-like attributes, can bend and twist. (Credit: NIST)
The chip, which possesses memristor-like
attributes, can bend and twist. (Credit: NIST)

Chips that are both flexible and do not break when dropped are highly prized in the electronics industry. However, straying from the consumer market, this new chip could also be adaptable in medical applications. For example, a patient requiring constant monitoring could be fitted under the skin with this chip, which will act as a sensor and will constantly monitor blood pressure or blood sugar levels. While there has been considerable research and development in the field of flexible circuits, no study has previously suggested using flexible memory.

The researchers at NIST strived to develop a memory that was not only practical, but cost efficient too. The process of developing such flexible memories starts with polymer sheets that are similar to transparencies used for overhead projectors. A thin layer of titanium dioxide is placed on the surface of the polymer and while the conventional method of depositing titanium dioxide requires the use of expensive equipment, NIST engineers employed a relatively inexpensive technique called “sol gel process.”

The titanium dioxide is spun in liquid form and then left to set. The team then adds electrical contacts to produce the flexible memory switch that can function on little less than 10 volts. The switch preserves its memory when power is discontinued, and still operates after being flexed over 4,000 times.

Memristors were first revealed in 1971, when Professor Leon Chua published a controversial paper stating that a component named ‘memristor’ should be included as the fourth fundamental circuit element together with the resistor, capacitor and inductor. Chua claimed that memristors had properties that could not be reproduced by any combination of the other three elements. A memristor could be represented as a resistor that modifies its resistance based on the level of current that flows through it. When power is stopped, the memristor retains this resistance.

“We wanted to make a flexible memory component that would advance the development and metrology of flexible electronics, while being economical enough for widespread use,” says NIST researcher Nadine Gergel-Hackett. “Because the active component of our device can be fabricated from a liquid, there is the potential that in the future we can print the entire memory device as simply and inexpensively as we now print a slide on an overhead transparency.”

TFOT has previously written about a method to print electronics with new silver-based ink that can be used in electronic and optoelectronic applications to produce flexible, stretchable, and spanning microelectrodes that transmit signals from one circuit element to another. More on flexible circuits can be found in our articles on paper chips and disposable electronics and HP’s memristor chip.

Additional information on the flexible memory chips can be obtained at NIST’s website.