This paper reports the development and characterization of a low-cost thin unimorph deformable mirror (DM) driven by positive voltage. The developed DM consists of both an inner actuator array and an outer ring actuator, which works two drive modes: the inner actuator array is used for aberration correction, while the outer ring actuator is used to generate an overall defocus bias. An analytical model based on the theory of plates and shells is studied for predicting the behavior of the developed DM. Measurement results indicate that dual direction maximum defocus deformations of the developed DM are -14.3 and 14.9 μm, respectively, and the resonant frequency is 1.8 kHz. The root-mean-square deformation of the mirror surface after correction is better than λ/20 for λ=633 nm. The replication of Zernike mode shapes up to the fifth order demonstrates that this developed DM is satisfactory for low-order aberration correction.