Manufacturing Bits: Nov. 21

Germanium-on-mica; foldable flash; HVPE.


Germanium is an element that can be used in various applications in electronics, such as optoelectronics, semiconductors and others.

For example, silicon-germanium (SiGe), an alloy of silicon and germanium, is used for making RF chips. In future finFET transistors, some are exploring the idea of using pure germanium for the PFET structure to boost the electron mobility in the device.

Rensselaer Polytechnic Institute (RPI) has put a new twist on germanium. Researchers have grown a germanium thin-film material on a substrate of mica. Mica is group of sheet silicate minerals, which are known for their basal cleavage properties.

In theory, germanium-on-mica enables a flexible template for efficient and cheap electronic and optoelectronic devices.

RPI grew germanium films about 80nm thick on muscovite mica substrates. The substrates are 75mm long, 25mm wide and 0.26mm thick. Researchers grew crystalline thin-film germanium based on a process called van der Waals epitaxy. They have been able to grow these films using an epitaxial or thermal evaporation process at 425 °C.

Germanium-on-mica (Source: RPI)

The arrangement of the germanium atoms are guided by van der Waals forces. This defines the attraction of intermolecular forces between molecules. “This is the first time strain-free van der Waals epitaxy of an elemental semiconductor has been demonstrated,” said Aaron Littlejohn, a doctoral candidate at RPI. “Our research found a narrow window, a very specific set of conditions that work.

“Our germanium film could be used as a thin-film nanomembrane, which could be integrated into electronic devices more easily than nanocrystals or nanowires,” Littlejohn said. “It could also serve as the substrate for the subsequent deposition of additional materials for flexible transistors and solar cells, or even wearable optoelectronics.”

Foldable flash
Using a chemical vapor deposition (CVD) process, the Korea Advanced Institute of Science and Technology (KAIST) has developed an ultra-flexible and foldable organic flash memory.

Flash memory, a non-volatile storage device, is typically associated with NAND and NOR. NAND flash is used for data storage, while NOR is aimed for code storage applications.

Developing a flexible flash device is desirable, but challenging. One of the big challenges is to develop high-performance flexible dielectric layers. These layers are used for the tunneling and blocking the charges.

KAIST has overcome these challenges. Researchers developed thin polymeric insulators using CVD. With the technology, KAIST produced flash memory with programming voltages around 10 volts. It has a data retention time of over 10 years.

Structure of flexible flash memory (Source; KAIST)

The device itself has a mechanical strain of 2.8%. Researchers fabricated the device on a 6-micrometer-thick ultrathin plastic film, which in turn makes it foldable. “This study well illustrates that even highly flexible flash memory can be made to have a practically viable level of performance, so that it contributes to full-fledged wearable electronic devices and smart electronic paper,” said Seunghyup Yoo, a professor of the School of Electrical Engineering at KAIST.

Foldable flash memory (Source: KAIST)

Kyma Technologies, a developer of wide-bandgap semiconductor material technologies, has developed a new hydride vapor phase epitaxy (HVPE) growth tool.

Kyma’s HVPE tool enables uniform and rapid growth of gallium-nitride (GaN) on a number of different substrates. HVPE has several advantages over metalorganic chemical vapor deposition (MOCVD).

This includes faster growth rates, lower cost starting materials, and a higher purity growth environment aided by the use of elemental group III sources instead of carbon containing metalorganic sources.

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