A surface sensor has been developed in order to record the cortical activity in animal models for neuro-science research. The device is made of gold on Cyclic Olefin Polymer (COP) and Cyclic Olefin Copolymer (COC) soft polymers using microsystems technology. The resulting system is flexible, customizable, bio-compatible, and fulfills reproducibility standards during the manufacturing process. Impedances are in the range of 100k Omega, thus making the system suitable for recording field potentials on the cortical surface. This paper explains the implementation process together with the implantation procedures and the results obtained in behaving rats. Results show that COP-based sensors are preferable to COC due to their higher flexibility and ease of manipulation. The versatility of COP polymers offers the possibility to adapt the electrode array to the cortical surface thus increasing surface of contact with the brain tissue. To validate the current approach, 8-contact sensors were implanted bilaterally over the motor cortices of awake, free moving rats. Cortical activity was evaluated on free moving animals and under the effect of different drugs. The quality and features of the recordings was in accordance with that of the current state of art systems thus demonstrating the feasibility of using COP-based systems for electrophysiological recordings in experimental investigation.