Dr. Zhi Chen's Group
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Dr. Zhi David Chen


Department of Electrical & Computer Engineering College of Engineering
University of Kentucky
453 Anderson Hall 
Lexington, KY 40506-0046 
Phone:(859) -218-6550
Fax : (859) - 257 - 3092
email : zhichen@engr.uky.edu

Electronic Devices and Materials 

-Exploring Future Photovoltaic Devices and Sensors-

Welcome to visit my group home page! It is a rewarding career in my research group. My current research focuses on studies of low-cost and high efficiency photovoltaic  devices utilizing novel nanoscale materials. One of the examples is the emerging perovskite materials. Our group has long experience in fabrication and characterization of semiconductor devices and sensors using novel nanoscale materials. The graduates in my research area are highly demanded in industry (See Group Member Page). I always need outstanding people! Please feel free to send me your resume. 

Dr. Chen's Research Accomplishment

Google Scholar Citation: http://scholar.google.com/citations?user=lW-EfMYAAAAJ&hl=en&oi=ao

TiO2 Nanotubes and Carbon Nanotubes. Dr. Chen had extensive experience in anodization of aluminum when he worked on humidity sensors in 1989-1992. In 2001, working with Dr. Dawei Gong, his postdoctoral research associate, and Prof. Craig A. Grimes who was then at Kentucky, he successfully created TiO2 nanotubes through anodization of pure titanium, a new type of inorganic oxide nanotubes. This idea came from his past experience in humidity sensor research using anodization. As the corresponding author, Prof. Chen first presented this work at Symposium Z3.9, 2001 MRS Fall Meeting, Nov. 26-29, 2001, Boston, MA, USA. The first author, Dr. Dawei Gong, moved with Prof. Craig A. Grimes to Penn State University, where the work was submitted to J. Mater. Res. with a wrong address of Prof. Chen, Wenchong Hu, and Suresh Singh. The paper entitled Titanium Oxide Nanotube Arrays Prepared By Anodic Oxidation” was published in J. Mater. Research 16, 3331-3334, 2001, Citation: >2,500 on Google Scholar. In addition, he and his co-workers fabricated the first vertically aligned carbon nanotube (CNT) arrays with high density and uniformity on silicon substrates using porous anodic aluminum oxide (AAO) as templates (“Growth of well-aligned carbon nanotube arrays on silicon substrate using porous alumina film as nanotemplate”, Appl. Phys. Lett. vol. 79, 3083-3085, 2001, Citation: >170 on Google Scholar; “Ethylene flame Synthesis of well-aligned multi-walled carbon nanotubes”, Chem. Phys. Lett. vol. 346, pp. 23-28, 2001, Citation: >210 on Google Scholar ). This provides a possibility for integration of carbon nanotube arrays with silicon electronics. The above research has a large impact on nanoscale material research community.

Lithium Doped TiO
2 for Low-Cost Perovskite Solar Cells. TiO2 is both a dielectric material and a wide bandgap semiconductor. Dr. Chen and his students developed Li-doped compact TiO2 layers used as electron transport layer in the planar heterojunction perovskite solar cells and achieved the photo conversion efficiency (PCE) of 17.1% with negligible hysteresis (Nano Energy 31 (2017) 462–468) (Citations: >150 on Google Scholars). Later he and his students found a “stitching effect” of Isopropyl alcohol/Chlorobenzene mixed anti-solvent in washing processes. This effect can be used to achieve large grain sizes of perovskite films. Isopropyl alcohol molecules play an important role in stitching cesium-containing triple cation perovskite grains so that more homogeneous morphology and lower defect density of perovskite films were achieved via this process. The solar cells exhibited a stabilized PCE of 19.2% (Nano Energy 39 (2017) 616–625) (Citations: >110 on Google Scholars).

Novel Humidity/Moisture Sensor. Dr. Chen invented humidity/moisture sensors based on alpha-alumina/silicon dioxide hybrid dielectric films. Unlike the regular humidity sensors, moisture sensors with very high sensitivity for sensing extremely low moisture levels (<1 ppm) or dew point <-76 deg celsus are very important for industrial processing and control. The worldwide market for this type of sensors is over 1 billion dollars. The mainstream moisture sensors used in dew point meters are porous gamma-phase aluminum oxide. Unfortunately, gamma-phase aluminum oxide experiences phase change from gamma phase to boemite. This phase change causes calibration drift of moisture sensors. The commercial gamma-phase aluminum oxide sensors have to be calibrated every six months. It is well known that silicon dioxide is a very stable dielectric material. Based on his experience in silicon dioxide research for MOS devices, Dr. Chen invented alpha-alumina/silicon dioxide hybrid dielectric moisture sensors, described in US Patent 8,739,623 (06/03/2014), US Patent 9,285,334 (03/15/2016), and Chinese Invention Patent 201410246545 (08/24/2016). This novel sensor is being commercialized in Advanced Semiconductor Processing Technology  LLC (ASPT USA), Lexington, Kentucky, USA. In December 2014, ASPT LLC secured $1M investment for product development and manufacturing scale up. The novel humidity sensor has been featured in the Electrochemical Society Interface Winter 2017 volume 26, issue 4, 67-70 (doi: 10.1149/2.F07174if). The products are dew point transmitters with three types: T100, T80, T60. His technical review about humidity sensors has made a large impact on humidity sensor research community (“Humidity sensors: a review of materials and mechanisms”, Sensor Letters vol. 3, 274-295, 2005,Citation: >1180 on Google Scholar).

Hydgogen/Deuterium (H/D) Isotope Effect. This effect was discovered in 1996 by Drs. Lyding and Hess at University of Illinois at Urbana-Champaign (UIUC). As a graduate student at UIUC, Dr. Chen helped develop this effect into a manufacturing process, so that integrated circuits (microchips) lifetime is dramatically improved (IEEE Electron. Dev. Lett., vol. 19, pp. 444-446, 1998IEEE Electron. Dev. Lett., vol. 21, no. 5, 221-223, 2000). In addition, the classical theory suggested that the hot-electron degradation of MOS transistors was caused by hot electron injection into the gate insulator (SiO2). Based on his  experiments using H/D isotope effect, Dr. Chen proved that it is not the hot-electron injection into the oxide but the hot-electron bombarding the SiO2/Si interface that causes the degradation, (On  the mechanism for interface trap generation in MOS transistors due to channel hot carrier stressing”, IEEE Electron. Dev. Lett., vol. 21, no. 1, 24-26, 2000). This laid a foundation for establishing a more accurate theoretical lifetime model for microchips, which is very important for the reliability of computers, cell phones, and iPods/iPads etc.