U.S. Made of Low-Voltage Flexible Circuits Made of Nanocrystals

General integrated circuits are printed on hard silicon wafers, but flexible and flexible circuits are used more widely. In today's ubiquitous electronic products, flexible electronic devices are more in line with popular needs, but finding a material with excellent performance and low cost is a major challenge. According to a report from the Physicist Organization Network on November 26, researchers from the University of Pennsylvania recently showed that a cadmium selenide nanocrystal can be "printed" or "coated" on soft plastic to make a variety of excellent performance. Electronic equipment. The related papers were published in the recent "Nature & Communications" magazine.

According to the director of the thesis, Xie Li Kakan, amorphous silicon is used on the displays of portable computers and other devices. According to the performance standards of cadmium selenide nanocrystals, the speed of carrying electrons is 22 times faster than that of amorphous silicon. In addition to speed, cadmium selenide has an advantage in deposition temperature: the process required for amorphous silicon operates at a high temperature of several hundred angstroms, and cadmium selenide nanocrystals can be deposited and softened at room temperature, enabling them to be used. More flexible plastic negatives. In addition, the researchers also chose a special ligand, which is a chemical chain that protrudes from the surface of the nanocrystals, enabling the electrical conductivity of the circuit to be pushed into the film.

"Although many people have studied the electron transport of cadmium selenide, they have not been able to use their excellent performance." said David King, a doctoral student in the Department of Materials Science and Engineering of the School of Engineering and Applied Science who led the research. "We study The innovation in the system is based on the use of new ligands that can be easily transferred to flexible plastics, while other bases will melt the plastic."

Nanocrystals can be dispersed in an ink-like liquid, so circuits can be made using a variety of deposition techniques. The researchers used a rotary spray method that pulled a thin layer of solution on the surface by centrifugal force. In addition, it can be done by dipping, spraying or inkjet printing.

The production process is to print the bottom electrode pattern on the soft plastic with a shadow plate, draw the line area, and then use the plate to define the upper conductive zone, and use a gold connection circuit. In addition, an insulating aluminum oxide layer and a 30 nanometer nanocrystalline coating are also added. Finally, the electrode is formed on the top layer by a film deposition method to form the final circuit. “Making complex circuits is like building a multi-story building. Gold is like a staircase, so that electrons can move between floors.” Kakan said.

The researchers used this process to make an inverter, an amplifier, and a ring oscillator, and tested the performance of nanocrystals in these three circuits. Dr. Lai Yuming, a Ph.D. student in the Department of Electrical and System Engineering at the School of Engineering, said: “The inverter is the basic device for building more complex circuits; the amplifier can amplify the signal in an analog circuit; the ring oscillator can be 'opened' in multiple stages of the digital circuit. 'Off' signal."

"The operating voltage of these circuits is only a few volts. If you want to use batteries to drive portable electronic devices, they must be low-voltage, otherwise they will not work." Kagan said that these cadmium selenide nanocrystal circuits combine flexibility The relatively simple manufacturing process and the advantages of low energy consumption paved the way for new devices, sensors and other applications in biomedical and safety applications. (Chang Lijun)

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