Research On The Piezoresistive Effect Of N-type Silicon Nanowires

Since the piezoresistive effect?PRE?of Si was first reported in 1954,strain-induced semiconductor property modulations has been observed and has been successfully used in pressure sensors and accelerators,which base on the relationship between the change in resistance and applied stress?strain?.As the size of the electronic integrated circuit continuing decrease and the discovery of low-dimensional semiconductor nanomaterials,people found that the nanomaterials have a higher tolerance to deformation and many unusual physical characteristics.Therefore,it is important to understand the piezoresistive effect of the nano-sale Si for the study of strain-induced semiconductor property modulation and the design of the micro-or nano-devices,which base on the piezoresistance of Si.In this study,The N-type<111>,<110>and<100>-oriented Si nanowires were prepared by using a focused ion beam?FIB?technique.By using a commercial scanning tunnelling microscope-transmission electron microscope?STM-TEM?joint instrument(Nanofactory^TM),inserted into a TEM,the piezoresistive property of Si nanowires have been studied deeply and systematically.Specific studies are as follows:1.In double beam?electron/ion?microscopy system,Si nanowires were directlycut from commercial N-type Si wafers?electrical resistivity was 1–10?cm?by using FIB technique.Then the Si nanowires were transferred and fixed to the Au tip,which is convenient to insert into a STM-TEM holder.2.Stresses were applied to individual Si nanowires,and their correspondingelectrical responses were simultaneously captured inside a transmission electron microscope.A well contact between the nanowire and the probe were achieved by using electron beam-induced deposition?EBID?technology,and reliable I-V curves were measured.The results are as follows:1)For<111>-oriented Si nanowires,tensile and compressive stresses wereapplied along the axial direction,results indicated that the resistances decrease continuously in both tensile and compressive processes,and the measured piezoresistance coefficient is same order of magnitude as its bulk counterpart,but smaller:-3.3×10^-1111 Pa^-1 and 1.9×10^-1111 Pa^-1 for tension and compression respectively.Finally,the circulatory properties was also investigated,results indicated that the Si nanowire is highly reproducible and has good stability in terms of stress-induced change in the electrical properties.2)For<110>-oriented Si nanowires,large-scale compressive strain wasachieved,and results show that the resistance decrease with strain increase obviously.Compared with the initial state the resistance decreased 93.7%,and the current increased 15 times.Finally the calculated piezoresistance coefficient is 9.42×10^-1111 Pa^-1 which is higher than<111>direction.3)For the<100>-orientation,different sizes microwires and nanowires wereprepared and studied.For the nanowire,the calculated piezoresistance coefficient is 25.84×10^-1111 Pa^-1 which is higher than other two direction.Found that resistance of microwire decrease with bent strain,and the final state decreased 48.7%.3.Compared and analyzed the orientation influence to the piezoresistive effect,the results show that the piezoresistive effect of N-type Si nanowire was affected by orientation greatly,and<100>is the most sensitive direction.However,the final piezoresistance coefficient is smaller than the bulk.The analysis suggests that the magnitude of the strain range is the main reason.Besides,the study also found that the electron beam did not change the tendency of current growth caused by strain.This study has an important reference value to the micro-or nano-devices,which base on the piezoresistance of Si.Moreover,it has a positive meaning for the study of strain-induced semiconductor property modulation.