Fabrication Method of 3D Feed Horn Shape MEMS Antenna Array. Using MRPBI System and Application for Microbolometer

Transcription

1 Fabrication Method of 3D Feed Horn Shape MEMS Antenna Array Using MRPBI System and Application for Microbolometer Jong-yeon Park*, **, Kun-tae Kim*, Sung Moon*, Jong-oh Park*,Myung-Hwan Oh*, James jungho Pak** *Microsystem Research Center, Korea Institute of Science and Technology P.O.BOX 131,Cheongryang, Seoul, , Korea **Dept. of Electrical Engineering, Korea University, Seoul, Korea ABSTRACT A 3D Feed horn shape MEMS antenna has some attractive features for array application, which can be used to improve microbolometer performance. Since MEMS technology have been faced many difficulties to fabrication of 3D feed horn shape MEMS antenna array itself. The purpose of this paper is to propose a new fabrication method to realize a 3D feed horn shape MEMS antenna array using a MRPBI(Mirror Reflected Parallel Beam Illuminator) system with an ultra-slow-rotated and inclined x-y-z stage. A high-aspect-ratio 300 µm sidewalls had been fabricated using SU-8 negative photo resist. It can be demonstrated to feasibility of realize 3D feed horn shape MEMS antenna array fabrication. In order to study the effect of this novel technique, the 3D feed horn shape MEMS antenna array had been simulated with HFSS(High Frequency Structure Simulator) tools and then compared with traditional 3D theoretical antenna models. As a result, it seems possible to use a 3D feed horn shape MEMS antenna at the tera hertz band to improve microbolometer performance and optical MEMS device fabrication. Keywords: MRPBI, 3D MEMS Antenna, Microbolometer, HARS, 3D UV-Lithography, IR image sensor 1. INTRODUCTION Recent advances in MEMS (Micro Electro Mechanical Systems) industries have given rise to the advent of various MEMS fabrication techniques to fabricate microstructures made from various materials. There is also a need for fabricating complicated 3-Dimensional micro structures with high aspect ratios, such as application for enhanced Microbolometer coupled with a 3D MEMS antenna array, enhanced optical efficiency of TFT-LCD and display devices * Correspondence: jypark@kist.re.kr; Phone: ,6758; Fax: ,6909

2 application. Although the 3D feed horn MEMS Antenna structure has many advantages, could not be carried out due to the difficulty of fabrication using conventional UV (Ultra-violet) lithography techniques. In this paper, a novel method to realize 3D feed horn MEMS Antenna array using MRPBI (Mirror Reflected Parallel Beam Illuminator) System is presented. 54 μm Antenna μm.5 μm Substrate Absorption layer Supporting leg Figure 1: Schematic drawing of 3D feed horn MEMS antenna coupled with Microbolometer.. CONCEPTS AND IMPLEMENTATION OF MRPBI SYSTEM The most difficult problem in HARS(High Aspect Ratio Structure) and 3D feed horn shape MEMS antenna array fabrication is how to exposure parallel beam using UV lithography apparatus. We know need to make parallel beam over 6meter UV light propagation ray path for 4 inch exposure area using CODE V optical simulator but usual laboratory height is smaller than 6 meter. Therefore, higher height apparatus is difficult to set up at usual laboratory. Lamp housing Rear reflector UV cold mirror Shutter, filter Optical board Sample stage Motor, gear, sensor Figure : Schematic drawing of MRPBI System

3 So we tried to solve the problem using UV light long propagation ray by several UV cold mirror reflection method. These results can be supported by fig. Schematic drawing of MRPBI System and fig.3 Configuration of MRPBI System. MIRROR MIRROR 7 4 HOUSING(AL PROFILE) 5 t STEEL 1 3 AIR OUT LAMP HOUSING REAR REFLECTOR UV COLD MIRROR 6 SHUTTER & FILTER OPTICAL BOARD SAMPLE STAGE MOTOR, GEAR & SENSOR 1. Lamp Module. Motorized stage 3. U.V cold Mirror 4. Cooling line 5. External housing 6. Optical board 7. Control box Figure 3: Configuration of MRPBI System Conventional UV-lithography apparatus have been exposed on the planar stage but MRPBI System exposure method is with a difference. For fabrication of more high aspect ratio 3D structure array, stage is x-y-z direction tilted, 360 automatic control rotated and exposure simultaneously. In consideration of more parallel UV light, MRPBI system exposure area is smaller than conventional UV-lithography apparatus. Mask coupled with a wafer can be employed - way vacuum fixed and it can be controlled to selection of hard contact, soft contact, and several contact conditions respectively using - way fixed vacuum system. Fig.4 show to inside photography of MRPBI system. Its rotational axis can be controlled two ways that first is manual controlled and second is computer controlled by RS-3C communication port. So we can change experiment parameter: rotation time and exposure time. MRPBI s wavelength is 365nm by 1kw SHP Hg lamp and radiation intensity can be changed to maximum 10mw/Cm.

4 Figure 4: Inside photograph of MRPBI System 3. OPTIMAL DESIGN OF 3D MEMS ANTENNA USING HIGH FREQUENCY STRUCTURE SIMULATOR The incident thermal, or blackbody, radiation emitted by all objects of a given physical temperature is a maximum at the 8-1 µm wavelength range. So we considered 3D antenna dimensions in relation to the development of a new form of IR imaging array that uses 3D feed horn MEMS antenna technology to couple the incident thermal radiation into an individual array element or pixel. Fig.8 shows optimal design parameter and incident light radiation pattern of 3D feed horn MEMS antenna using HFSS(High Frequency Structure Simulator). Following equations (1),(),(3) are relative to conical feed horn antenna and equation (4),(5),(6) are relative to feed horn antenna optimal design and simulation. D ( db) = 10log c C 10 ε ap 10 s 4π λ ( πa) = 10log L( ) λ 3 L( s) = 10log10( εap) ( s + 6.5s 17.79s ) dm s = 8λl (1) () (3) a : Radius of horn at the aperture L(s): directivity loss of aperture efficiency C : aperture circumference s : maximum phase deviation

5 L 0. 3 cosθ = λ 1 cosθ (4) d m 0.6 sinθ cosθ = λ 1- cosθ (5) d L= m (6) sinθ L: Feed horn length Dm: Feed horn diameter Following Fig 5, fig.6 and fig.7 are to 3D Cylinder MEMS antenna simulation, 3D Conical horn MEMS antenna simulation and 3D feed horn MEMS antenna simulation respectively. Fig 5,fig.6 and fig.7 are scattered radiation pattern. This result indicated the side lobe by miss tuning 3D MEMS antenna modeling. 100 Figure 5: 3D Cylinder MEMS antenna simulation using HFSS(High Frequency Structure Simulator) Figure 6: 3D Conical horn MEMS antenna simulation using HFSS(High Frequency Structure Simulator)

6 Figure 7: 3D Feed horn MEMS antenna simulation using HFSS(High Frequency Structure Simulator) Fig.8 shows optimal design of 3D feed horn MEMS antenna using HFSS(High Frequency Structure Simulator). The result indicated that directivity is 0.4 db and gain is 0.77 db. Feed horn angle parameter is 11.5 and feed horn diameter is µm Figure 8: Optimal design of 3D feed horn MEMS antenna using HFSS(High Frequency Structure Simulator)

7 Table. 1 Simulation numerical value of 3D feed horn MEMS antenna design using HFSS (A unit Diameter & Length: µm) Diameter Length Gain(dB) Diameter Length Gain(dB) Table 1 is indicated that 3D feed horn MEMS antenna simulation numerical value using HFSS. Fig.9 shows comparison of 3D MEMS antenna directivity gain. Consequently, directivity gain of feed horn shape is highest about db Directivity(dB) Cylinder Conical Feed Horn Horn Figure 9: Comparison of 3D MEMS antenna directivity

8 4. FABRICATION PROCESS OF MICROBOLOMETER COUPLED WITH 3D FEED HORN MEMS ANTENNA ARRAY USING MPRBI SYSTEM 1. Seed Layer Deposition. Exposure with Tilt+Rotation, Develop 3. Electroplating 4. CMP Process 5. PR remove 6. Seed Layer Remove 7. Antenna Separation Figure 10: Process sequence for micro fabrication of 3D feed horn MEMS antenna Fig.10 is illustrated fabrication main process procedure of 3D feed horn MEMS antenna array. Process procedure: 1.Seed layer deposition,.feed horn antenna mold fabrication using MRPBI system, 3.Electroplating process, 4. CMP(Chemical mechanical polishing) Process; Planarization, 5. Photoresist remove, 6.Seed layer remove, 7.Antenna separation. 5. EXPERIMENTS & RESULT Thick Photoresist Figure 11: SEM image and schematic drawing of negative photoresist PMER lithography experiment using conventional lithography apparatus

9 Figure 1: SEM images of vertical sidewall array using negative photoresist PMER by MRPBI system Figure 13: SEM images of inclined sidewall array using negative photoresist SU-8 by MRPBI system Fig.11 shows that negative photoresist PMER experiment result using conventional UV-lithography apparatus. In Fig.1 we can see over 100µm vertical sidewall structure array using negative photoresist PMER. The condition are step spin coating: (500rpm/s, 600rpm/s), stabilization: 5min, prebake: 110!C/5min, PEB(Post Exposure Bake): 100!C/15min and exposure time is 1800sec. When expoure time is over 400sec that happen to serious hard reflection. Following fig.14 is show that look like teapot shape array SEM images (a),(b) and D microscope picture (c). In this case, experiment parameters are 0û inclined stage, y-axis direction 360º rotated and exposure time is 1800sec. The exposure time is the most important factor in this experiment.

10 (a) (b) (c) Figure 14: SEM images (a),(b) and D microscope picture(c) of teapot shaped array using negative photoresist PMER by MRPBI system 6. CONCLUSION Novel techniques and methods have been described to fabrication of 3D feed horn MEMS antenna using a new UV lithography apparatus called MRPBI(Mirror Reflected Parallel Beam Illuminator) system in this paper. And proposed to optimal 3D MEMS antenna design for coupled with Microbolometer using HFSS(high frequency structure simulator). ACKNOWLEDGMENTS The authors wish to acknowledge that this paper is a result of the research accomplished with the financial support of the Intelligent Microsystem Center, Seoul, Korea, which is carrying out one of the 1st century's New Frontier R&D Projects sponsored by the Korea Ministry Of Science & Technology. REFERENCES [1] E. L. Dereniak "Infrared detectors and systems", John Wiley & Sons, Inc [] Paul W. Kruse, David D. Skatrud "Uncooled Infrared Imaging Arrays and Systems" Semiconductor and Semimetals, Vol. 47, Academic press, 1997 [3] M. A. Gallo, D. S. Willits, R. A. Lubke, E. C. Thiede " Low cost uncooled IR sensor for battlefield surveillance ", SPIE Vol. 00 Infrared Technology, pp ,1993 [4] Paul W. Kruse," Uncooled IR Focal Plane Arrays ", SPIE Vol. 55 Infrared Technology, pp , 1995 [5] N.Butler, R.Blackwell, R. Murphy, R. Silva and C. Marshall, " Low Cost Uncooled Microbolometer Imaging System for Dual Use ", SPIE Vol. 55 Infrared Technology, pp ,1995

11 [6] K.C. Liddiard, " Thin film monolithic detector arrays for uncooled thermal imaging ", SPIE Vol Infrared Technology, pp , 1993 [7] I. A. Khrebtov and V. G. Malyarov "Uncooled thermal IR detector arrays", J. Opt. Technol. 64(6), pp.511-5, 1997 [8] B.E.Cole, R. E. Higashi, and R. A. Wood " Monolithic Two-Dimensional Arrays of Micromachined Microstructures for Infrared Applications" Proceeding of the IEEE, Vol 86, pp , 1998 [9] R. A. Wood, " Uncooled thermal imaging with monolithic silicon focal plane ", SPIE Vol. 00 Infrared Technology, pp. 3-39, 1993 [10] Peter L.Marasco and Eustace L. Dereniak, " Uncooled Infrared Sensor Performance ", SPIE Vol. 00 Infrared Technology, pp , 1993 [11] Hubert Jerominek, Timothy D. Pope, Christine Alain, Rose Zhang, " pixel uncooled bolometric FPA for IR detection and imaging ", SPIE Vol. 3436, pp , 1998 [1] A.Rogalski, Infrared Detector, goldon and breach science publishers, pp [13] A.P.Gruzdeva, V. Yu. Zerov, O. P. Konovalova, Yu. V. Kulikov "Bolometric and noise properties of elements for uncooled IR arrays based on vanadium dioxide films" J. Opt. Technology. 64(1), pp. 7-80, 1997 [14] V.A.Kuznetsov and D. Haneman " High Temperature coefficient of resistance in vanadium oxide diodes ", Rev. Sci. Instrum. 68(3),pp , 1997 [15]E.E.Chain, "The influence of deposition temperature on the structure and optical properties of vanadum oxide films", J. Vac. Sci. Technol. A 4(3), pp ,1985 [16] C. H. Griffiths and H. K. Eastwood " Influence of stoichiometry on the metal semiconductor transition in vanadium dioxide", J.Appl. Phys. Vol.45, No. 5, pp , 1974 [17]E. L. Dereniak "Infrared detectors and systems", John Wiley & Sons, Inc.1995 [18] Larry F. Tompson, Introduction to Microlithography second edition.