# Recent Progress in Pressure Sensors for Wearable Electronics: From Design to Applications
## 5 Conclusion and Future Perspectives  
In this review, recent progress in flexible pressure sensors was introduced, covering their transduction mechanisms, fabrication methods, and applications. The pressure sensor is one of the most demanded electronic devices in wearable electronics, artificial skin, and other fields. Various studies have been conducted, and substantial effort has been devoted to enhancing the electrical performance of sensors. Excellent electrical performance, especially high sensitivity, can broaden the application of the device.  
Regardless of the type of sensor, the future trends of sensor development mainly focus on the following aspects. First, high electrical performance, including sensitivity, response time, detection limit, and mechanical durability with a wide measurement range, is necessary. In general, highly-sensitive pressure sensors have a very small detection limit, but a narrow measurement range. In order to apply these sensors to wearable electronics with various quantities of external stimuli, it is essential to have a high sensitivity and a wide measurement range. In addition, hysteresis should be sufficiently secured for easy calibration. The mechanical durability for long-term use should also be guaranteed. Second, a multifunctional sensor is required to meet the needs of applications in the fields of wearable electronics. Unlike a laboratory where the environment is precisely controlled, people's surroundings  
Figure 9: Various types of sensor arrays. (**a**) CNT microyam-based sensor array. Reproduced with permission from [153], Copyright (2015), Wiley-VCH. (**b**) MWCNT/PDMS composite. Reproduced from [140]. (**c**) SWCNT-embedded PDMS with pyramidal patterns. Reproduced with permission from [154], Copyright (2018), Wiley-VCH. (**d**) Ag NW-embedded wavy PDMS. Reproduced with permission from [134], Copyright (2015), Royal Society of Chemistry.  
vary widely. Various external factors, such as humidity, temperature, vibration, etc., are present, and in order to produce truly wearable electronics, it is necessary to measure all external stimuli. In particular, although only the pressure sensor was covered in this review, the multifunctional sensor that measures both pressure and strain is required because they always act simultaneously on human skin. Third, self-powered sensors are a new trend in the field of wearable electronics in recent years. Piezoelectric and triboelectric pressure sensors are good candidates to realize this function. Overcoming the brittle properties of the piezoelectric materials is the main challenge for piezoelectric pressure sensors. The triboelectric pressure sensor further needs an increased power density. As wearable electronics develop, the device size and power requirements will decrease, but the triboelectric nanogenerator usually generates insufficient power density. In addition to the above trends of future developments, biodegradable and self-healing pressure sensors are desired for a wider range of wearable electronics applications. Further focused research is demanded to discover more flexible, stretchable and yet effective sensing materials. Moreover, to realize these diverse requirements, a novel fabrication method is likely required for future applications.  
Writing--original draft preparation, Y.K.; writing--review and editing, Y.K. and J.H.O.; supervision, J.H.O. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea Government (MSIP) (No. 2019R1A2C1005023). This work was also supported by the research fund of Hanyang University (HY-2020-0389).  
The authors declare no conflict of interest.