XII INTERNATIONAL CONFERENCE AND SEMINAR EDM’2011, SECTION IX, JUNE 30 - JULY 4, ERLAGOL 327 Micromechanical IR-Systems Georgy L. Kuryshev A.V. Rzhanov Institute of Semiconductor Physics, SB RAS, Novosibirsk, Russia Abstract – The results of experimental investigation of the membrane matrix mikrofotoconvectors, operation of which is based on the mechanical movement of the membrane plane are presented. The possibility of thermal radiation registration by optical methods in the visible spectrum was shown. Index Terms – Infrared, hybrid, membrane. I. INTRODUCTION HE AIM OF THIS project is to develop technology for production of membrane matrices of mikrofotoconvectors, operation of which is based on mechanical movement of the membrane plane [1]–[8], suspended on the support (bracket), due to difference in thermal expansion coefficients of binary system of metal- insulator transition. The main problems to be solved are the following: 1. To develop the technology for production of the so- called "sacrificial" layer. This layer determines the gap between the suspended membrane and the substrate and should not be destroyed during the subsequent production of the membrane, but then removed without destroying the structures formed. 2. To develop the technology for metal and dielectric layers ensuring production of heat-sensitive membranes. For development of this technology the existing technological processes for production of metal and dielectric layers were used. In addition to this, some new processes were developed. The topological pattern and the suspended construction were formed using photolithography process on the basis of specially designed test patterns. Chemical, plasma and gas etching processes were used. Two sets of photo masks including a wide range of design options for membrane cells, were designed and manufactured. Structures for measuring capacitance were produced using the second set. This allows us to estimate the gap between the membrane and the substrate, as well as to measure mechanical properties of the layers (resistance to bending). II. TASK SETTING Selection of materials that form the membrane system was based on the following requirements. The metal layer (suspended membrane) should have maximum coefficient of thermal expansion (CTE) and maximum thermal conductivity, as well as minimal mechanical stress – the condition necessary to ensure high sensitivity of the membrane matrix. Furthermore, surface of the metal plate exposed to incident radiation should absorb incident light as full as possible, whereas the opposite side of the metal surface of the membrane should reflect as full as possible (i.e. it should be mirror surface). The insulator, from which bracket providing suspension of the metal membrane is to be made, must have minimum coefficient of thermal expansion with minimal thermal conductivity and be free of internal defects. In addition, it must be resistant to multiple mechanical bending and provide support adhesion to the substrate. There must be good adhesion between the layer of metal and insulator. Both layers must be compatible with the photolithography process for forming the desired topological pattern and design in general. The latter requirement must be fulfilled by material of the "sacrificial" layer. The platform should be made of mechanically strong and chemically inert material transparent to visible light. In addition, it must be optically homogeneous and provide minimal distortion into the observed pattern, since signal pickup should occur through the substrate, III. RESULTS. MANUFACTURING TECHNOLOGY. Fig. 1. Fragment of the cell of the microfotoconvector obtained using atomic force microscopy instrument Solver P-47H. The figures are given in microns (in the plane of the structure, X and Y) and in nanometers (axis Z). In order to develop the technology for the suspended structure the aluminum layers obtained by thermal spraying were used. Silicon nitride synthesized in the RF- discharge plasma at 150ºC was used as the support for the metal membrane (bracket). To obtain suspended metal membranes the thermal spraying of copper and silver, as well as electrolytic deposition of silver were practiced. For manufacture of T ISBN 978-1-61284-795-5/11/$26.00 ©2011 IEEE XII INTERNATIONAL CONFERENCE AND SEMINAR EDM’2011, SECTION IX, JUNE 30 - JULY 4, ERLAGOL 328 more rigid brackets two new processes were developed: Silicon nitride layers were deposited by plasma in the reactor by planar-induction type. Carbonitride layers that were more solid as compared with silicon nitride layers were produced by gas deposition in remote plasma. Other materials with high coefficients of thermal expansion (CTE) were searched for. The technology for production of suspended structures made from these materials was developed. In order to determine optimum thickness of each layer and the optimum ratio of thicknesses of layers, which served as the basis of mikrofotoconvectors, deformation of the two-layer plate was theoretically evaluated. In order to eliminate the influence of operations aimed at production of membrane systems, the technology for removal of the sacrificial layer and photolithography processes was optimized. Measurement of thermal element was carried out by matrix camera of the visible range with the introduction of images into the computer in real time. For this the optical bench was designed based on the MII-4 and Metam P1. For the purpose of absolute calibration, comparison with the interference method of registration, as well as for absolute calibration of spatial displacement of a thermal sensitive element the test bench was designed to measure small capacitance (about 0.1 pF) on the basis of the bridge circuit. Flat membranes suspended on the bracket and parallel to the bearing base were fabricated. The materials, from which they are made, should differ in CTE. Due to this difference in CTE, the membrane move parallel to the base plate. The proposed optical method for registration of change in displacement value allows creating a new type of IR detector operating at room temperature. Figure 1 shows fragments of cells of the microphotoconvector made on the basis of the aluminum nitride silicone with removal of the sacrificial layer by gas etching. The image was obtained by atomic force microscopy based on Solver P-47H instrument. To ensure high sensitivity of membrane structures they should be made of materials with minimal mechanical stress. High adhesion to underlying surfaces is required. Material of the bracket and the membrane must be resilient and resistant to repeated mechanical bending. The topological pattern and the suspended construction were formed using test patterns and photolithography processes with chemical, plasma and gas etching. In order to produce the metal suspended membrane (material with high CTE), aluminum, copper and silver layers produced by thermal vacuum deposition, as well as electrolytically deposited silver films were used. Nitride, carbide and silicon carbonitride layers produced by the method described above were used as the support (bracket) of the metal membrane. The gap between the pedestal and the bracket was set by thickness of the sacrificial layer and ranged from 0.3 microns to 0.55 microns. The spread over the layer thickness does not exceed 10%. Either amorphous silicon or silicon dioxide layer produced in the low-pressure reactor at 100°C was used as sacrificial layer. The latter layer was removed with wet etching after manufacturing of the structure. The amorphous silicon layer was etched by gas etching with xenon fluoride. The Al2 O3 substrate was used as the platform. It is mechanically strong, chemically inert and transparent in the visible region. An additional electrode was formed for manufacture of the structures designed to measure capacitance of microfotoconvectors. The electrode was formed on the surface of the carrier base before the deposition of the "sacrificial" layer. It was manufactured by "explosive" photolithography on the indium oxide (III) layer. The transparent conductive In2O3 layer was deposited by ion- plasma sputtering through spraying with argon ions from In2O3 )with SnO2 additive). This electrode does not interfere with visual inspection both for removal of the "sacrificial" layer, and quality of the metal membrane surface. Thickness of the insulating layers was measured using ellipsometer LEF-3M with wavelength of 0.6328 nm based on monocrystalline silicon satellite. Thickness of amorphous silicon was evaluated during growth based on interference fringes. Thickness of metal layers and the gap between the suspended membrane and the carrier base were estimated using the interference microscope MII-4. Curvature of the surfaces was evaluated by distortion of the fringe using MII-4. Completeness of the removal of "sacrificial" layer and quality of the metal membrane surface were monitored through the transparent sapphire pedestal. IV. DISCUSSION In order to determine optimum thickness of each layer and optimum ratio of the thickness of the layers, on which mikrofotoconvectors are based, deformation of the plate consisting of two layers was theoretically evaluated. 1 The experimental samples were produced on the basis of the optimized basic processes and the processes developed for this project. The membrane sensitive to heat was obtained for SiC systems (T = 300ºC, 400ºC) - Ni-Ag and SiC (T = 300ºC, 400ºC) – Ni-Ag-polyamide-6. The gap between the suspended membrane and the substrate was 0.2–0.4 μm. 2. It was shown that registration of thermal radiation was conducted by optical methods in the visible spectrum. 3. Test patterns and methods for measurement of capacitance between the suspended metal membrane and the conducting substrate were designed. This technique allows high-precision recording of spatial gap between the photosensitive element and the substrate and quantitative measurement of thermal element. The quantitative evaluation of thermal sensitivity (15–20 nm /�C) based on capacitance and optical techniques coincides taking into account the margin of error. VI. CONCLUSION In order to achieve the required thermal sensitivity parameters for modern infrared matrix elements (0.1ºC at frequency of 25 frames per second), it is necessary to further optimize the design of the suspended membrane and the existing technological processes (in particular, the KURYSHEV et al.: MICROMECHANICAL IR-SYSTEMS… 329 developed technology of two-layer structures based on organic polymer films with high CTE). In addition, mechanical properties of process films and changes of them during production of structures must be studied in detail. REFERENCES [1] J.P. Salerno, “High frame rate imaging using uncooled optical readout photomechanical IR sensor”, Proc. SPIE 6542, 65421D (2007). [2] W. Carr and D. Setiadi, “Micromachined pyrooptical structure”, US Patent No. 6,770,882 (2004). [3] L. Secundo, Y. Lubianiker, and A.J. Granat, “Uncooled FPA with optical reading: Reaching the theoretical limit”, Proc. SPIE 5783, 483–495 (2005). [4] A. Flusberg and S. Deliwala, “Highly sensitive infrared imager with direct optical readout”, Proc. SPIE 6206, 62061E (2006). [5] A. Flusberg, S. Swartz, M. Huff, and S. Gross, “Thermal� �to�visible transducer (TVT) for thermal�IR imaging”, Proc. SPIE 6940, 694015 (2008). [6] M.Wagner, E.Ma, J. Heanue, and S.Wu, “Solid state optical imag- ers”, Proc. SPIE 6542, 65421P (2007). [7] M. Wagner, “Solid state optical imaging: Performance update”, Proc. SPIE 6940, 694016 (2008). [8] D. Grbovic, N.V. Lavrik, and P.G. Datskos, “Uncooled infrared imaging using bimaterial microcantilever arrays”, Appl.Phys. Lett. 89, 073118 (2006). Georgy L. Kuryshev was born in 1945 in Novosibirsk. In 1967 he graduated from the Novosibirsk State University. In 1987 he received a Doctor of phys.-math. sci. degree. Since 1967 he has been a staff member of the Institute of Semi- conductor Physics, Siberian Branch of the Russian Academy of Sciences (ISP SB RAS). At present he is the Head of the Physical Basics of Integral Microe- lectronics Laboratory. Email:
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