Abstract
The liquid crystal mixture E7, based on cyanobiphenyl, has been successfully employed to map electric field strength and distribution in AlGaN/GaN high electron mobility transistors. Using a transmitted light image through crossed polarizers the optical response of the liquid crystal deposited onto the surface of the devices was recorded as a function of source–drain bias, Vds. At a critical voltage of 4V the preferred direction of orientation of the long axes of the liquid crystal molecules in the drain access region aligned with one of the polarizers resulting in reduced transmitted light intensity. This indicates that at this electric field strength molecule orientation in most of the liquid crystal film is dominated by the electric field effect rather than the influence of surface anchoring. The experimental results were compared to device simulations. Electric field strength above the surface at Vds=4V was simulated to reach or exceed 0.006MV/cm. This electric field is consistent with the field expected for E7 to overcome internal elastic energy. This result illustrates the usefulness of liquid crystals to directly determine and map electric fields in electronic devices, including small electric field strengths.
Highlights
AlGaN/GaN high electron mobility transistors (HEMTs) have been the focus of intensive research to deliver improved device reliability in recent years [1]
In this work it is demonstrated that liquid crystal can be used for electric field analysis of electronic devices, on the example of AlGaN/GaN HEMTs
A decrease in light intensity with the increased applied source–drain bias, i.e. with increasing electric field strength, is visible. This decreasing light intensity with applied bias demonstrates the optical response of the orientation of the liquid crystal director, which aligns parallel to the applied electric field and one of the polarizers if enough energy is provided to overcome the effect of surface anchoring of the liquid crystal molecules
Summary
AlGaN/GaN high electron mobility transistors (HEMTs) have been the focus of intensive research to deliver improved device reliability in recent years [1]. Devices exhibit high internal electric fields and high channel temperatures, well in excess of traditional semiconductor device systems These can trigger degradation and generation of electronic traps [7]. While liquid crystals have been used in the past to image temperature distribution and hot spots in the devices [18] their potential to image electric fields in electronic devices has been ignored to date. This is despite their wide scale use in displays that exploit their orientation under an electric field [19]. This is done by using their ability to orientate with electric field lines in the nematic phase rather than exploiting a phase change
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
