| Flexible electronics are promising for information technology,which have been ubiquitous in providing measurement information event through physical contact.Up to now,although many kinds of flexible sensor devices have been reported,some problems have not been investigated in detail,such as the sensing mechanism,stability,limit measurement etc.Previous studies indicate that the bending failure mechanism of flexible electronic devices in complicated environment is one of the problems that need to be addressed.In this paper,Polydimethylsiloxane(PDMS)-graphene oxide(GO)-Ag nanoparticle(NPs)devices are studied by changing the structures and parameters of the functional layer,and controlling the temperature condition to provide critical insight into temperature effects on piezoresistive properties and bending endurance of flexible memory devices.Corresponding temperature dependent fatigue failure mechanisms of the flexible devices are revealed.Firstly,GO sheets were embedded into PDMS elastomer,then functional layer and Ag electrodes were fabricated by thermosetting and vacuum evaporation coating,respectively.The addressable Ag/PDMS-GO/Ag device focused on the effect of structure and parameters on the piezoresistive properties of composite films.The results showed that the structure and parameters played key roles in device characteristics.The device with double side micro-pattern structure,lwt%of GO and 200μm thickness showed the best performance in sensitivity(R/Ro for 10-2)and response time(2×102 ms).The charge transfer is dominated by GO and the distance between neighbor GO sheets under press are reduced enough to form a conductive path,resulting in the decreasse of the response resistance and achieving pressure detection.Secondly,the Ag/PDMS-GO/Ag devices with best performance were selected and the effect of doped Ag NPs on the piezoresistive properties were systematically investigated.The results showed that doping Ag NPs can significantly improve the properties of the device.The Ag/PDMS-GO-Ag NPs/Ag devices performed best with doping concentration of 1.0 wt%or 1.5 wt%and 50 nm Ag NPs,it’s R/R0 reach 10-3 and the response time is about 7×101 ms.First-principles calculations found that the band gap was reduced by 1.07 eV after the introduction of Ag into the GO segment.The good dispensability of Ag NPs can effectively increase the probability of formation of conductive pathways.The Abaqus simulation of PDMS-GO-Ag NPs composite revealed that the functional layer and the substrate showed elastic mismatch under press.The distance between conductive fillers is gradually reduced to form a conductive path,and stress concentration occurs preferentially at the microstructure.The deformation of the microstructure increases the effective contact area and change the contact resistance.Finally,the Ag/PDMS-GO-Ag NPs/Ag devices were selected and the temperature dependent piezoresistive performance of device under bending condition was investigated.The results showed that bending at variable temperature may exacerbate the deterioration of the characteristics of the device.In general,bending effects on the deterioration is significantly stronger than temperature effects on charge transport.In the range of 20℃ to 0℃,the decrease in temperature reduces the carrier activity,inhibits the charge transport process and the sensitivity is slightly reduced.Further reducing the temperature to-40℃,the sensitivity decreases linearly.The low temperature increased the brittleness of the organic and inorganic materials in the device and the flexibility is deteriorated.Under the continuous mechanical bending,the surface of the device is more likely to initiate microcracks.For comparison with low temperature bending condition,the temperature raised from 20℃ to 60℃,the thermal expansion of the elastomer material makes it easier to deform under pressure,which can improve the bending resistance of the device.When the temperature is higher than 60℃,due to the difference in physical properties of the polymer molecules and inorganic NPs,the interfacial adhesion of the elastomer decreases,and the microcrack density increases under bending,which deteriorates the performance of the device.This paper makes up for the research gaps in the performance degradation of flexible electronic devices in multiple environments.In this paper,the piezoresistive properties,temperature-dependent bending endurance and mechanism of PDMS-GO-Ag NPs composite are systematically studied.The deterioration process of the temperature dependent bending endurance is revealed,and the physical mechanism is clarified. |
