High temperature silicon-carbide-based flexible electronics for monitoring hazardous environments
Graphical abstract
Introduction
Recent advancements in soft-lithography and printing technologies have made tremendous progress in the development of stretchable and bendable electronics, providing new exciting functionality over conventional hard, rigid platforms ([Jeong et al, 2018], Rogers et al., 2010, Nathan et al., 2012, [Phan et al, 2019a], [Falahi et al, 2019]). A broad range of flexible applications have been translated from basic-research into commercial products, including bendable displays, smart-watches for biometric-data tracking, and wearable ultraviolet dosimeters. Although organic materials and conductive polymers offer the intrinsic bendable property, most of the commercialized devices are built based on conventional inorganic semiconductors which are transferred from the rigid substrates onto a soft and flexible template (Sun and Rogers, 2007, Liu et al., 2015). The use of common inorganic semiconductors such as silicon and III-nitride takes advantage of their advanced fabrication technologies as well as the established physics ([Yu et al, 2017], [Zhang et al, 2019]).
Typical flexible applications operate at a small temperature range varying from room temperature to approximately 150 °C (Jeon et al., 2013, [Dinh et al, 2019], [Dinh et al, 2017], Zhan et al., 2014). Recent studies suggests an increasing demand for devices that can operate at a wider range of temperatures varying from cryogenic up to several hundred degree Celsius ([Almuslem et al, 2019], [Sun et al, 2018], [Chen et al, 2016], Li et al., 2015). This is quite obvious in space exploration industry, where the temperature can be reduced to below −250 °C for the case of Jupiter or can reach to above 400 °C on Venus surface (Phan et al., 2018, Hunter et al., 2006, [So and Senesky, 2017]). NASA has been taking part in developing a host of deployable structures including balloons, solar sails, space-borne telescopes and membrane-based synthetic aperture radars to work at these temperatures (Brandon et al., 2004, [Brandon et al, 2011], [Basirico et al, 2017]). To develop each of these applications, a thin, low mass, large area structure (i.e., polymer-based) is an imperative component. Additionally, integration of sensors within these structures is of significant importance. Furthermore, considering the fact that every milligram launched to space does matter for the associated cost, having electronics devices on a light-weight, flexible platform could ease the installation and significantly reduce the launching expense (Meador, 2019). Aside from high temperatures, chemical/mechanical corrosion and high radiation are other hazardous factors that can adversely affect the performance of flexible electronics. Well-known examples for these extreme conditions are deep sea exploration and underwater environmental monitoring systems, where salty water could rapidly degrade device performance ([Nassar et al, 2018], [Shaikh et al, 2019]). As a consequence, there is a need for developing niche electronics that can withstand these extreme environments.
Main-stream flexible inorganic devices have been developed based on silicon (Si) nanothin films. Nevertheless, due to its relatively fast hydrolysis rate, Si electronics gradually degrade when being subjected to a long-term underwater operation (Yin et al., 2015, Hwang et al., 2015). Furthermore, at high temperature the thermally activated intrinsic carriers make the performance of Si-based devices no longer reliable (Li et al., 2018). Silicon carbide (SiC) has emerged as an excellent alternative owing to its robust physical properties ([Phan et al, 2019b], Mandrusiak et al., 2018, [Yang et al, 2019b], [Nguyen et al, 2017]). Silicon carbide-based transistors, pressure sensors, photodetectors operating in extreme environments have been successfully demonstrated ([Lanni et al, 2013], Nguyen et al., 2018, [Yang et al, 2019a]). However, as these devices were built either in the bulk-form or from a SiC epilayer on a solid substrate (Qamar et al., 2015), SiC-based electronics with mechanical flexibility that can operate at high temperatures have been rarely reported.
We present here ultra-thin silicon carbide (SiC) nanomembranes on a soft, thin polyimide substrate as a robust platform for flexible electronics working in harsh environments, taking advantage of the electrical stability and chemical inertness of the SiC material. The low mechanical bending stiffness of SiC nanomembranes combined with the intrinsic softness of micro-thick polyimide enable excellent flexibility. As a proof of concept, we demonstrate an Al-doped SiC film on polyimide as a temperature sensors that can work above 400 °C, the highest working temperature reported so far on flexible electronics based on wide-band-gap materials.
Section snippets
Preparation of SiC films
We deposited the 3C-SiC films on both sides of a 6-in. (100)-silicon wafer using a hot wall chemical vapor deposition chamber at 1250 °C. Prior to the growth process the silicon wafer was cleaned using the RCA standard. The deposition process started with a carbonization step to form a growth-buffer layers. Silane and propane were then alternatively supplied to stack SiC layers onto the buffer layer. Trimethyaluminum (TMAl) was employed to form a normally doped p-type 3C-SiC with a carrier
Results and discussion
Fig. 2 shows photographs of the fabricated devices. The large scale of the SiC-Si platform (Fig. 2(a)) along with the compatibility with standard micromachining processes could enable wafer-scale level fabrication of flexible SiC electronics. The transparency of released SiC nanomembranes (Fig. 2(b)) allow for the alignment of subsequent photography masks with the pre-defined free-standing structures. The simulation results (Comsol Multiphysics™) shown in Fig. 2(d) indicates that under
Conclusion
This work reports on the development and characterization of flexible crystalline silicon carbide sensors operating at elevated temperatures up to 450 °C. The experimental results showed the high feasibility of transferring silicon carbide nanothin films from the hosting Si substrate onto a soft platform, enabling the integration of SiC-based flexible electronics. The experimental data indicated a good bonding adhesion between SiC and polyimide, with excellent mechanical flexibility and
Authors’ contribution
H.-P.P., T.D. fabricated the devices. H.-P.P. and T.N. conducted the thermosensitive measurement. T.-K.N., A.Q. did the FEM simulation. H.P.P. and J.H. took the SEM images. All authors analyzed the experimental results. H.-P.P. and N.-T.N. designed and supervised the project. The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.
Conflict of interest
None declared.
Acknowledgments
This work was partially funded by the research grants LP160101553 andDE200100238 from the Australian Research Council (ARC). The 3C-SiC material was developed and supplied by Leonie Hold and Alan Iacopi of the Queensland Microtechnology Facility, part of the Queensland node, Griffith of the Australian National Fabrication Facility, a company established under the National collaborative Research Infrastructure Strategy to provide nano and microfabrication facilities for Australia's researchers.
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