Manufacturing And Characterization Of Contacts In High-performance Polymer Transistors

In the past decades,with the intensive research on organic semiconductor,organic field-effect transistors(OEFTs)have fast emerged owing to their unique advantages of low manufacturing cost,high flexibility and large scale fabrication.Nowadays,OFETs play important role in organic electronics so that they can be applied to many applications like integrated circuits,biology and sensing,which is highly valuable to our daily life and to scientific research.Previously,most of high-performance organic semiconductors used for OFET are single-crystal or polycrystalline small molecules,yet they are not suited for the applications demanding high flexibility in particular for rollable electronics.With constant development of organic electronics,polymer semiconductors have also been used in the fabrication of OFET.However,high-performance polymer field-effect transistors are relatively little studied,especially the transistors based on the new donor-acceptor conjugated polymers which were reported to sensitive to contact effects.The contacts can be affected by the method of fabrication and the deposition rate,causing the problem of contact resistances,thus affecting the performance of the device such as threshold voltage and mobility.Based on above context,the main research content of this thesis is to use thermal evaporation and sputtering to manufacture Ag contacts for OFET with bottom-gate and top-contact architecture,which are based on donor-acceptor conjugated polymer semiconductor.When using thermal evaporation,three different evaporation rates of 0.1 (?)/s,0.5 (?)/s and 1.0 (?)/s were chosen as a comparison,whereas three different sputtering powers of 10 W,20 W and 30 W were selected when using the sputtering.Later,the semiconductor parameter analyzer connected with probe station was used to extract the transfer characteristics and the output characteristics of transistors,as well as to analyze the device performance.Finally,the performances of the devices manufactured by thermal evaporation and sputtering were compared under the same deposition rates.After characterization,it is noticed that,regardless of thermal evaporation and sputtering for contact manufacturing,as long as a lower deposition rate is used,the contact effect is minor and the thus the device performance is superior.Compared with high evaporation rates,the contact resistance of transistors fabricated at low evaporation rates decreases by 33% and the threshold voltage decreases about 5 V.Meanwhile,the mobility of the device with low evaporation rate increases by three times.Similarly,compared with high-power sputtering,the contact resistance of low-power sputtering decreases by 60% and the threshold voltage decreases 9 V,as well as the mobility increases by six times.Under the same deposition rates,sputtering is found to be able to optimize the metal-semiconductor contact,highly improving charge injection and charge transport.For example,the contact resistance is reduced further by 50%,threshold voltage decreases 7 V,and the mobility is doubled in comparison with those made by using sputtering.