Graduate Student Research Assistantship available in the area of chalcogenide devices and memories. Please contact kriscampbell@boisestate.edu for information.
Research area: Electronic Memories and Devices Made with Chalcogenide Materials
Chalcogenides are materials containing at least one of the elements sulfur, selenium, or tellurium. For the past 30 years, chalcogenide materials have allowed significant technological advancements to be made in the areas of photodetection, energy storage, chemical sensing, and data storage (1-3). One of the best examples of a technology that uses chalcogenide materials is optical data storage. In DVD’s and CD’s (used for digital video, data, and music storage), the data is optically ‘stored’ in the chalcogenide material. The development of DVD’s and CD’s has revolutionized the entertainment industry.
In the application of light detection, chalcogenide materials have historically provided the best efficiency in the conversion of light to an electric current as well as the widest range of detectable light wavelengths. Some of the common chalcogenide photodetection materials used for infrared-light detection include PbSe, PbS, and HgCdTe.
The use of chalcogenide materials for the application of electronic memory has been under study for over three decades (4). While the material has been successfully developed for optical data storage, we have not yet realized its commercial use in electronic data storage. Our ultimate goal is to use chalcogenide electronic memory to replace the existing electronic memories, Flash and DRAM, and to create a ‘universal’ memory for all of our electronic devices (computers, phones, games, etc.). However, the engineering implementation of these materials as electronic memories has been slow with relatively little research taking place in the area of materials selection.
Recently, there have been significant contributions to the development of chalcogenide electronic memory arrays and devices (5-8). This research has been driven by the fundamental limitations of the existing Flash and DRAM technologies, limitations which have underscored the need for a new memory technology (the biggest limitation is scaling). The chalcogenide memory array research has typically focused on one type of chalcogenide material (Ge2Sb2Te5) with minor compositional modifications made to this material to try and improve or alter the electronic switching properties. These contributions have renewed the scientific and engineering interest in the study of new chalcogenide materials that show the potential to be used as electronic memories. Desirable properties of these materials include the ability to switch with low current, with fast switching pulses, exhibit a large number of switching cycles (> 1010) and retain data at a variety of operational temperatures for at least a couple of years when disconnected from a power supply.
In addition to not being held to the scaling limitations of DRAM and Flash memory, chalcogenide electronic memory has the advantage of being radiation resistant, unlike DRAM and Flash memory (8). This type of memory is thus of interest to NASA for inclusion in instruments used in the radiation harsh environment of space.
In our research, we are primarily studying chalcogenide materials for use in electronic memory. In addition, we are creating novel electronic devices comprising chalcogenide materials which exhibit unique current-voltage characteristics and thus have the potential to be developed into new electronic devices (e.g. resonance tunnel diodes, sensors, optical detectors). In this work, we are investigating the relationship between chalcogenide material properties and memory switching properties by measuring the electronic switching properties of memory devices built using chalcogenide glasses with differing glass compositions. The specific aim of this work is to understand and predict the relationship between material properties and the electronic memory switching properties such as data retention, speed, power requirements, and number of possible switching cycles in order to build an electronic chalcogenide memory device. Understanding the relationship between memory properties and material properties will allow us to design custom memories with specific switching characteristics.
1. Tanaka, K. “Chalcogenide Glasses” in Encyclopedia of Materials: Science and Technology, 2000, pp. 1-9.
2. Popescu, M. “Disordered Chalcogenide Optoelectronic Materials: Phenomena and Applications”, J. Optoelectronics and Advanced Mat,. 7 (2005) 2189-2210.
3. Vassilev, V.S.; Boycheva, S.V. “Chemical Sensors with Chalcogenide Glassy Membranes” Tantala 67 (2005) 20-27.
4. Ovshinsky, S.R. “Reversible Electrical Switching Phenomena in Disordered Structures” Phys. Rev. Lett. 20 (1968) 1450-1455.
5. Ahn, D.-H.; Kang, D.-H.; Cheong, B.-k.; Kwon, H.-S.; Kwon, M.-H.; Lee, T.-Y.; Jeong, J.-h.; Lee, T.S.; Kim, I.H.; Kim, K.-B. “A Nonvolatile Memory Based on Reversible Phase Changes Between fcc and hcp” IEEE Electron Device Letters, 26 (2005) 286-288.
6. Cho, W. Y.; Cho, B.-H.; Choi, B.-G.; Oh, H.-R.; Kang, S.; Kim, K.-S.; Kim, K.-H.; Kim, D.-E.; Kwak, C.-K.; Byun, H.-G.; Hwang, Y., Ahn, S.; Koh, G.-H. Jeong, G.; Jeong, H.; Kim, K. “A 0.18-um 3.0-V 64-Mb Nonvolatile Phase-Transition Random Access Memory (PRAM)” IEEE J. Solid-State Circuits, 40 (2005) 293-299.
7. Hellemans, A. “A New Phase in Nonvolatile Memory?”, IEEE Spectrum, June 2005, 18.
8. Maimon, J.D.; Hunt, K.K.; Burcin, L.; Rodgers, J. “Chalcogenide Memory Arrays: Characterization and Radiation Effects”, IEEE Transactions on Nuclear Science, 50 (2003) 1878-1884.
Research area: Nonvolatile memories based on perovskites, oxides, carbon, and electron spin. Research description coming soon.
