Research On Design,Fabrication Of Microlens Array And Integration Between Microlens Arrays And CCD Image Sensors

With the development of modern optics, the researchers of the world in this field are attaching more and more importance to the investigation and applications of micro-optic elements in many fields. The microlens arrays are the important kind of micro-optics elements. This dissertation places emphasis upon the design theory, fabrication technology and optical performance measurement of microlens arrays. And it emphasizes the researches on integration technology between microlens array and CCD (charge coupled device) image sensors, which can improve the detecting performances of image sensor remarkably. The primary content of the dissertation includes: (1) The development of micro-optics and the kind of micro-optics elements have been summarized. And the statuses in quo of fabrication technology and applications of microlens array and present research on the integration between microlens and CCD image sensors have been introduced. (2) Optical design theory of microlens array is introduced. It includes the geometrical optics design theory for refractive microlens and diffraction optics theory for diffractive microlens. The dispersion effect of diffractive and refractive microlenses has been analyzed theoretically. Base on the rigorous vector diffraction theory, the diffractive mechanism of subwavelength structure has been discussed. Furthermore, the effect of fabrication-related errors on the diffractive microlens array and the optical losses in the system are also studied. (3) There are often the microlenses with low sag and long focal length in the applications. With regard to this kind of microlenses, a design method, the surface directly quantized, has been introduced. By this method, the microlens in the CCD applications has been designed effectively. It avoids finite phase steps, which appears when the microlens is designed by conventional design method. So the diffractive microlens array can keep high diffractive efficiency. (4) Based on MEMS(Micro-Electro-Mechanical-System)technology, the fabrication processes, including photolithography and pattern transfer are discussed. Especially the reactive ion etching (RIE)technology with three ingredients SF6/O2/CHF3 has been investigated deeply and the perfect patterns on the silicon substrate are achieved. At the same time, the polymer microlens array is studied and fabricated. High quality microlenses are completed. (5) The measurement system and testing method of microlens array are introduced. With this system, the microlens parameter such as point-spread function (PSF), diffractive efficiency, focal length and so on, can be evaluated effectively. The errors and influencing factors have been analyzed. (6) In the integration system of microlens and CCD, the microlens is used as field lens. The optical analysis of microlens convergent efficiency is carried out so as to optimize the optical coupling. (7) The integration between diffractive microlens array and 256×256 element PtSi IRCCD has been highlighted. With the microlens integrated, the fill factor (FF) of IRCCD increases evidently. And the IRCCD image sensors operating at 77K indicate an approximate 2-fold increase in relative optical responsivity in the spectral range of from 3μm to 5μm. At the same time, the integration technology between microlens array and visible is investigated. The monolithic and hybrid integration method is introduced, respectively. In sum, the innovations included in the dissertation are as follow: (1) As regard the design theory of microlens, the design method of continuous surface quantized by 2N equal phase for the microlens with low sag and high F-number has been put forward. It not only keeps the diffractive efficiency of microlens with low sag high, but also allows the microlenses with low sag to be made by binary optics fabrication technology. (2) The microlens array is made from the polymer with high transmissivity in the visible band, such as polyimide, BCB, SU-8 photoresist and is applied in the integration between microlens and visible CCD image sensors. (3) In order to evaluate the optical quality of microlens effectively, a testing system is set up and the wave band of microlens can cover 190～1100nm。(4) The hybrid integration between quartz microlens and visible 516×516 element CCD image sensor has been explored.