The TIKI instrument is a next generation 10-micron cryogenic extreme adaptive optics (ExAO) imager being designed for the Gemini South telescope. Its goal is to detect the thermal emission of Earth-like planets in orbit around Alpha Centauri A or B. TIKI is also a prototype for future TMT instruments capable of imaging Earth like planets around a larger star sample, and performing low spectral resolution characterization to search for biomarkers on detected planets. The science module will operate at cryogenic temperature in order to minimize thermal background, dominant in the 10-micron wavelength range. The instrument will use Adaptive Optics, a vortex coronagraph, focal plane wavefront sensing, and advanced post-processing techniques to reach a 1E-7 contrast in less than 200 hours of observing time. It aims to be background-limited in the 2-5 lambda/D zone, which corresponds to the habitable zone around the two Sun-like stars of the Alpha Centauri system. In this paper, we give an overview of the project goals, present TIKI's conceptual optical design, and summarize preliminary simulation results.