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Conductive polymer holds promise for next generation organic electronics

Conductive polymer holds promise for next generation organic electronics

tech innovation 2022

The concept illustration shows the highly moving electrons across the polymer. credit: Brian Long

For decades, field-effect transistors enabled by silicon-based semiconductors have driven the electronics revolution. But in recent years, manufacturers have faced further reduction in size of silicon chips and tougher physical limits to achieve efficiency. In this, scientists and engineers are looking for an alternative to the traditional metal-oxide semiconductor (CMOS) transistor.

“Organic semiconductors offer several distinct advantages over traditional silicon-based semiconductor devices: they are composed of abundantly available elements such as carbon, hydrogen, and nitrogen; they offer mechanical flexibility and low cost of fabrication; and They can be easily fabricated on large scales,” notes UC Santa Barbara engineering professor Yon Wiesel, part of a group of researchers working with the new material.

“Perhaps more importantly, the polymers themselves can be fabricated using a variety of chemistry methods to endow the resulting semiconductor devices with interesting optical and electrical properties. These properties can be attributed to inorganic (for example, can be designed, tuned or selected in a number of ways (silicon based) transistors.”

The design flexibility that Wiesel describes is exemplified in the reconfigurability of the devices, reported by UCSB researchers and others in the journal. advanced Materials,

Reconfigurable logic circuits are of particular interest as candidates for post-CMOS electronics, as they make it possible to simplify circuit design while increasing energy efficiency. In contrast to carbon-based (eg, silicon- or gallium-nitride-based) transistors called organic electrochemical transistors (OECTs), a recently developed class has been shown to be well suited for reconfigurable electronics.

In a recent paper, chemistry professor Thuk-Kwyn Nguyen, who leads the UCSB Center for Polymer and Organic Solids, and co-authors including Wiesel describe a breakthrough material – a soft, semiconducting carbon-based polymer – which can provide unparalleled benefits. Inorganic semiconductors are currently found in conventional silicon transistors.

“Reconfigurable organic logic devices are promising candidates for the next generations of efficient computing systems and adaptive electronics,” write the researchers. “Ideally, such devices would be of simple structure and design, [as well as] Power-efficient and compatible with high-throughput microfabrication techniques.”

conjugation to conductivity

A conjugated polyelectrolyte, or CPE-K, consists of a central conjugated backbone with alternating single and double bonds, and several charged side chains with anions. “Having conjugated bonds throughout the polymer makes it conductive, because the delocalized electrons have high mobility along the length of the polymer,” explains lead author Tung Nguyen-Dang, a postdoctoral researcher in Nguyen’s lab co-advised by Wiesel. “You’re marrying two classic materials, a polymer and a semiconductor, in this molecular design.”

Artificial Intelligence (AI) played a role in developing the content. “You can proceed by trial and error to create a material,” Nguyen says. “You can make a whole bunch of them and hope for the best, and maybe one in twenty works or has interesting qualities; however, we worked with a professor at California State Northridge, Gang Lou , who used AI to select the building blocks and calculate them to get a rough idea of ​​what to do next, given the energy levels and properties we were aiming for.”

reconfiguration detection

A major advantage of the CPE-K is that it enables reconfigurable (“dual-mode”) logic gates, meaning they operate in either reduction mode or accumulation mode by adjusting the voltage at the gate. To be switched on the fly. In reduction mode, the current through the active material between drain and source is initially high, before any gate voltage (aka on state) is applied. When gate voltage is applied, the current drops and the transistor is switched to the OFF state. Accumulation mode is the opposite—without gate voltage, the transistor is in an off state, and applying gate voltage generates a higher current than switching the device to the on state.

Nguyen says, “Traditional electronic logic gates, which are the building blocks for all digital circuits found in a computer or smartphone, are hardware that do only one thing for which they are designed.” “For example, an AND gate has two inputs and one output, and if the inputs applied to it are all 1, the output will be 1. Similarly, a NOR gate also has two inputs and one output, but if If all inputs applied to it are 1, the output will be 0. Electronic gates are implemented using transistors, and reconfiguring them (eg changing from AND gate to NOR gate) requires aggressive modification, e.g. That solution, which is usually too complicated to be practical.

“The reconfigurable gates, as we show, can behave as both types of logic gates, switching from AND to NOR and vice versa by simply changing the gate voltage,” he continues. “Currently in electronics, functionality is defined by structure, but in our device you can change the behavior and make it something else by changing the voltage applied to it. If we were to extend this invention from a gate to a more complex circuit Out of many such reconfigurable gates, we can imagine a powerful piece of hardware that can be programmed with many more functionalities than traditional ones that contain the same number of transistors. “

Another advantage for CPE-based OECTs: they can be operated at very low voltages, making them suitable for use in personal electronics. That, along with its flexibility and biocompatibility, make the material a potential candidate for implanted biosensors, wearable devices and neuromorphic computing systems in which OECTs can serve as artificial synapses or non-volatile memories.

“Our collaborators are building tools that can monitor the drop in glucose levels in the brain that occurs just before a seizure,” explains Nguyen, a colleague at the University of Cambridge in England. “And after detection, another device—a microfluidic device—will deliver a drug locally to stop this process before it happens.”

According to Nguyen, devices made of CPE-K feature concurrent doping and de-doping depending on the type of ions. “You build the device and put it in a liquid electrolyte—sodium chloride” [i.e., table salt] dissolves in water,” she says. “You can then drive sodium to move into the CPE-K active layer by applying a positive voltage to the gate. Alternatively, you can change the polarity of the gate voltage and drive the chloride to move to the active layer. Each scenario produces a different type of ion injection, and those different ions are what allow us to change the way the device operates.”

Self-doping also simplifies the manufacturing process by removing the extra step of adding dopant. “Many times when you add a dopant, it is not distributed evenly across the volume of the material,” Nguyen says. “Organic doping materials tend to cluster together rather than disperse. But because our materials don’t require that step, you don’t run into the issue of uneven dopant distribution. You also avoid the whole process of optimizing and determining the dopants.” There are perfect mixes and proportions, all of which add up to steps and complicate processing.”

The team also developed a physics model for the device that explains its mechanism of action and correctly predicts its behavior in both operation modes, thus showing that the device is doing what it is doing.

Wiesel concluded, “This remarkable new transistor technology ideally exemplifies the amazing electronic and computing functionalities that are being enabled through convergent research in chemistry, physics, materials and electrical engineering.”

Logical switching using a single molecule

more information:
Tung Nguyen-Dang et al, Dual-mode organic electrochemical transistor based on self-doped conjugated polyelectrolytes for reconfigurable electronics (Adv Mater. 23/2022), advanced Materials (2022). DOI: 10.1002/adma.202270170

Provided by University of California – Santa Barbara

Citation: Conductive polymers hold promise for the next generation of organic electronics (2022, 23 June) retrieved 23 June 2022 from

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