Research On The Fabrication Process Of Micro Coaxial T-Shaped Power Divider

Power divider is an important element of RF microwave system.With the continuous development of RF microwave system to miniaturization,high frequency and high integration,higher requirements to power divider were put forward.Micro coaxial T-shaped power divider has good application prospects in RF microwave system due to its advantages of small volume,wide band and low crosstalk,but the manufacturing process of it not very mature.In this paper,the manufacturing process of micro coaxial T-shaped power divider was studied.Firstly,according to the structural features of T-shaped power divider,the processing scheme was decided,and then,the experiments was carried out on the technique difficulties,finally,the T-shaped power divider was fabricated combining with formulated processing scheme and previous experimental results.The problem of bad sidewalls verticality of AZ 50 XT photoresist mold was studied.The method of “pre-exposure” was used to solve the problem that the exposure dose cannot be selected accurately in the process of micro channel exposure;the problem of hard to photolithography caused by excessive light absorption coefficient of AZ 50 XT film was overcome by exposure and develop in twice;before developing the film,the passive layer that exist in the photoresist surface was removed through plasma treatment,eliminating the surface inhibition effect and reducing the difficulty of develop.After taking the above measures,the sidewall steepness of AZ 50 XT photoresist mold has been greatly improved.In order to solve the problem that inner conductor is liable to separate from SU-8 supporter,the interfacial bonding property between inner conductor and supporter was studied.By analyzing the interface of inter conductor and supporter,concluding that the bonding strength between inner conductor and supporter is decided by the bonding strength between inner conductor and seed layer,and then,a method that by adding titanium adhesive layer to improve bonding strength was proposed and relevant experiments were carried out.The experiment results showed that the bonding strength between the copper seed layer and supporter increases by 312% after adding the titanium adhesive layer,which proved the feasibility of this method.In order to explore the mechanism that adhesive layer can improve the interface bonding strength,the surface tension of SU-8 and contact angle between SU-8 and copper and titanium were measured,the adhesion work between SU-8 and copper and titanium were computed.The results showed that adhesion work between SU-8 and titanium is greater than that between SU-8 and copper,and the mechanism of adhesion layer can improve bonding strength was explained from the angle of adhesion work.According to the experiment results,a micro-coaxial T-shaped power divider which has a size of 7.7mm×3.9mm×210μm with a minimum size of 40μm was fabricated.In the fabrication process,by adding a photolithography process after micro-electroforming,the difficulty of measuring the height of copper deposits was solved;by adding the photoresist's thickness of masking layer,the over etching problem of seed layer was solved,and the dimension error that produced in the fabrication process of power divider is reduced by using the photo mask dimension compensation method.