Institute of Physics has made progress in research on ultra-sensitive molybdenum disulfide humidity sensor
Due to its ultra-high surface-to-body ratio, excellent electrical properties, and flexibility, two-dimensional materials have shown great promise in the field of humidity sensors. Among them, the transition metal chalcogenide represented by molybdenum disulfide provides the possibility for its application in electronic devices due to its excellent current switching ratio, mobility, and other characteristics. Since molybdenum disulfide is an n-type semiconductor itself, when its surface adsorbs water molecules, it is equivalent to its p-type doping, its electrical properties will show a corresponding change, using this principle can be used to sense The humidity sensor of the outside water molecular weight changes. At present, the research on molybdenum disulfide humidity sensor is mainly subject to the contamination of the surface of the material caused by the residual glue introduced into the process itself, which affects the adsorption of water molecules, resulting in problems such as low sensitivity or long response time. Therefore, how to obtain a molybdenum disulfide humidity sensor with high sensitivity and fast response time becomes the most important factor restricting its application.
In response to these problems, Dr. Zhao Zhao from the N07 Group of Nanophysics and Devices Laboratory, Institute of Physics, Chinese Academy of Sciences/Beijing National Laboratory for Condensed Matter Physics, under the guidance of researcher Zhang Guangyu, used a new gold stripping method to obtain clean The surface of the molybdenum disulfide field effect transistor, thereby achieving a sensitive response to water molecules. This processing method mainly uses the force between the molybdenum disulfide and the gold far greater than the force between the gold and the substrate, so that the excess molybdenum disulfide sample can be completely peeled off from the substrate, and at the same time ensured. The molybdenum disulfide surface used for the device is clean. This method can effectively avoid the influence of residual adhesive on the device performance after reactive ion etching in the process, and on the other hand greatly simplifies the processing process. The molybdenum disulfide field-effect transistor with an ultra-clean surface has significantly improved optical and electrical properties. From another aspect, it has been proved that the sample obtained by this processing method has better performance.
Since the molybdenum disulfide field-effect transistor obtained by using this gold stripping method has an ultra-clean surface, it can be sensitive to changes in external humidity, and greatly improves the sensitivity of the molybdenum disulfide humidity sensor. For the doping of water molecules, with the increase of humidity, the current of the device is significantly reduced. When the relative humidity changes from 0% to 35%, the resistance has an increase of nearly 104, compared to the previous molybdenum disulfide humidity sensor. The study has nearly three orders of magnitude improvement, and the corresponding mobility and current switching ratio also decrease linearly with increasing humidity. In addition to its ultra-high sensitivity, because the surface of molybdenum disulfide has no dangling bonds, the adsorption of water molecules is a pure physical adsorption, so the device can be easily desorbed, effectively reducing the response time and recovery time, respectively, up to 10s And 60s, and this device has a very good recovery performance, after a month of testing its initial resistance does not change, with a longer service life. In addition, molybdenum disulfide, which is benefited from CVD growth, can be formed into a uniform film and can be processed to obtain a series of molybdenum disulfide humidity sensor arrays with excellent performance, thereby positioning the spatial distribution of different humidity in the outside world. Monitor changes in the outside humidity distribution. In addition, the molybdenum disulfide humidity sensor with ultra-high sensitivity can still work well on flexible substrates, and its performance is basically not changed by the change of the applied stress, so that it can be applied to the field of flexible electronic devices in the future. may.
This humidity sensor based on ultra-clean surface molybdenum disulfide samples has high sensitivity, short response time and recovery time, long service life, high spatial resolution, and can be widely used in future non-contact positioning systems and two-dimensional materials Multifunctional flexible sensor array field. Related results were published in "Advanced Materials." This work has been funded by the Chinese Academy of Sciences' Special Category B Strategic Pilot Science Project and the National Natural Science Foundation of China.
Figure 1. (a) Process of device processing using gold stripping method. (b) Molybdenum disulfide field effect transistor array light maps fabricated on a silicon oxide substrate.
Figure 2. (a) Changes in output characteristics of molybdenum disulfide field-effect transistor with increasing humidity. (b) The change in the transfer characteristic with increasing relative humidity. (c) Correspondence between resistance change and relative humidity.
Figure 3. Time response characteristics of molybdenum disulfide humidity sensor. (a) The response time and decay time of the molybdenum disulfide humidity sensor in the case of a single humidity pulse are ~10s and ~60s, respectively. (b) Life test of molybdenum disulfide humidity sensor.
Figure 4. Spatial response characteristics of molybdenum disulfide humidity sensor. (a) When the finger is near the molybdenum disulfide humidity sensor, the resistance of the device increases exponentially with decreasing distance. (b), (c) are the resistance distribution values ​​of the device array in response to the external humidity distribution, and the calculated relative humidity values.
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