rus
Issue #6/2013
P.Gindin, V.Karpov, N.Kuznetsov, V.Petrenko, V.Semenov, V.Chishko
Photodetector arrays and subarrays
Photodetector arrays and subarrays
OAO Moskovsky Zavod SAPFIR, a manufacturer of thermal imaging systems, starts the production of the second generation of products that are used in special tasks of observation, control, aiming, guarding of the military and civilian objects. Nomenclature, design concept and main characteristics of the developed batch-oriented devices are given in this article.
Теги: ir equipment photodetectors second generation thermal imaging devices ик-техника матричный фотоприемник второго поколения тепловизионные приборы
Transformation of the object thermal radiation into its visible image is the foundation of thermal imager operation. Due to their thermal radiation the obscured or hidden objects become visible. Imaging IR equipment dynamically progresses due to the capacity to recognize the objects despite the level of natural illumination. Therefore, the main condition of functionality of these devices is the temperature contrast between the image details. The main structural unit of imaging IR devices is the focal plane array of photodetectors (FPA). Analog signals from the array pixels after transformation into the digital form enter the processing unit where the video signal is formed. In modern photodetector arrays permissible temperature contrast up to 0.02 K is reached. Known high-efficient IR-photodetectors based on multi-layer structures with quantum wells require deep cooling of array down to the deep cryogenic temperatures for their operation (Т≈65 K) and microbolometric detector arrays require good thermal stabilization on the basis of thermoelectric cooling. Besides, microbolometric detector arrays have limits in temperature sensitivity (ΔТ≈0.07 K) at low frame frequencies (Fк≈30 Hz).
SAPPHIRE Moscow Plant OJSC traditionally manufactures the products designated for the thermovision and thermal direction finding systems. Semiconductor IR photodetectors and photoreceiving devices based on Si, Ge, indium antimonide (InSb), cadmium-mercury-tellurium (CdHgTe) (CMT) can be marked out among them. In 2008-2010 the company was developing the second generation of batch-oriented fast-response photoreceiving modules (PRM) for the prospective imaging IR equipment [1-5]. The purpose of this development was to create industry-oriented constructions and technology of the second generation of infrared PRM assembly: PRM subarrays with the format 4×288 elements and PRM arrays with the format 320×240 and format 320×256 elements.
The work was being performed for the modernization and import substitution of PRM in imaging infrared channels for the control and observation complexes with different purposes. As a result the following PRMs of the second generation were developed:
unified PRM arrays with the format 320×240 and format 320×256 elements for the range 3-5 µm (ФУК 149М and ФУК 154М);
unified PRM subarrays with the format 4×288 elements for the range 8-10.5 µm functioning in two-pass mode of time delay and integration (ФУК 148М and ФУК 152М);
unified PRM arrays with the format 320×256 elements for the range 8-10.5 µm (ФУК 143М and ФУК 151М).
STRUCTURE OF PHOTORECEIVING MODULES
Developed PRMs are constructed on the basis of single-type scheme. It includes:
array or subarray of photosensitive elements (APSE) on the basis of photodiodes of InSb or CMT;
silicon large-scale integration (LSI) reading circuit (multiplexer) hybridized by indium microcontacts with APSE and ensuring the reading, previous amplification and multiplexing of APSE signals;
vacuum cryostatic body where APSE, silicon LSI circuit, getters and coolable diaphragm with optical filter ensuring the specified spectral sensitivity range are located;
microcryogenic system (MCS) of cooling.
PHOTODETECTOR ARRAYS BASED ON InSb
Photodetector arrays based on indium antimonide (InSb) are designated for the operation within the spectrum region of 3-5 µm. The photodetector arrays with the format 320×240 elements and format 320×256 elements with the line-frame reading organization were designed.
APSE [4] is developed on the basis of indium antimonide photodiode array with fine base region on silicon supporting template. APSE construction (Fig. 4) ensures the harmonization by thermal expansion coefficients of both elements – APSE and silicon LSI reading circuit (multiplexer). As a result, the influence of thermal mechanical stress on hybrid assembly of APSE with silicon LSI reading circuit is minimized.
Silicon LSI reading circuit (Fig. 2) is developed according to the CMOS technology with the design rules of not more than 0.8 µm [4]. LSI circuit has the necessary functional capabilities. First of all, it ensures the operation mode upon which the concurrent reading (for 4/8 yields) of complete frame with the format 320×240 elements with high sensitivity and frame frequency of not less than 200 Hz. Secondly, the reading mode of several lines has high sampling frequency (of not less than 8000 Hz). Thirdly, it determines the mode of "window" with squared shape dimensions of which are set from outside with the multiplicity by sides of 8 pixels ("window" is situated in the required place of array field).
Photodetector array is formed by the hybridization of APSE with silicon LSI reading circuit with the help of indium micropillars (Fig. 3) which are obtained via the operations of "dry" etching. Then, using the adhesive binding the photodetector array with temperature sensors is placed on the contact raster (Fig. 4) which in turn is the cryostat coolable element.
PHOTODETECTOR ARRAYS AND SUBARRAYS BASED ON CADMIUM-MERCURY-TELLURIUM
The main material for manufacturing of fast-response photodetectors with the spectral range 8-14 µm and limit characteristics of sensitivity is the solid solution of cadmium and mercury tellurides CdXHg1-XTe (CMT).
Constantly progressing the CMT manufacturing was being developed starting from the method of growth of bulk crystals from the melt at high temperature and finishing the methods of low-temperature epitaxy. Epitaxial methods are the most applicable for the growth of CMT layers with large area and creation of photodetector arrays respectively. The main methods of their obtaining are liquid-phase epitaxy (LPE) and molecular-beam epitaxy (MBE). In the Institute of Semiconductor Physics of Siberian Branch of the Russian Academy of Sciences (ISP SB RAS) the home equipment was manufactured and production-oriented technology of molecular-beam epitaxy of layers of CMT-based strategic material of modern IR equipment for the spectral range 8-14 µm was developed (ТУ 1778-003-03533808-2003).
When developing the photoreceiving module arrays and subarrays with the range 8-10.5 µm certain types of photodetectors were used.
Linear photodetector (subarray) ФП2 is the hybrid assembly on indium micropillars of photodiode subarray of CMT hetero-epitaxial structures grown by the method of molecular-beam epitaxy (HES CMT MBE) and silicon LSI circuit (multiplexer). PD is the coolable linear photodetector array with the format 288×4 elements – analog of ID TL015-XX-V3 photodetector manufactured by Sofradir Company. Assembly is designed in the ISP SB RAS [6]. Construction of the linear photodiode array is demonstrated in Fig. 5 and layout of photodiodes location in photoreceiving area is shown in Fig. 6.
Developed silicon LSI circuit (multiplexer) for ФП2 with the format 288×4 has the circuit and construction which peculiarities are: complete digital control using the parallel and series ports, deselection of any invalid cell and implementation of the function of bi-directional scanning. Hybridization of linear photodiode array with multiplexer is accomplished with the help of indium micropillars (Fig. 7).
Photodetector array ФП2М which was developed and manufactured in the ISP SB RAS represents the coolable CMT photodetector array with the format 320×256 elements with the pixel dimensions 30×30 µm [7]. Its long-wavelength cutoff is 10.5 µm. The construction of hybrid assembly of ФП2М photodetector is given in Fig. 8, and the format of receiver photosensitive field is shown in Fig. 9.
Construction diagram of photodetector array in vacuum cryostat
The construction of vacuum cryostat body (VCB) includes holder with fixed coolable elements, body with getter and cover with entrance window [1].
Simultaneously VCB holder is the tube of displacer of gas cryogenic refrigerator (GCR) which is included in the structure of MCS. The ceramic tip (contact raster) which is the mounting seat for photosensitive elements and other coolable elements of construction is secured on the edge of tube-holder. Assembly of the photodetector in VCB structure is given in Fig. 10.
The tip bond sites are connected with the bond sites of ceramic-metal base by the conductors (with diameter of 0.03 mm) of platinum (80%)-iridium (20%) alloy. Such connection ensures the optimal correlation between heat conductivity and electrical resistance.
Vacuum pumping of cryostat is performed through the copper exhaust tube inserted by the "solid" brazing (braze ПСР-72). After the pumping the exhaust tube is cut by the special wire cutter. It provides the cold (diffuse) welding of exhaust tube walls thus sealing hermetically the vacuum volume of VCB. Periodically activating the getters which are located on the inner wall of VCB maintaining or even restoration of the required vacuum in cavity is obtained if it will be necessary. Photodetector array in the structure of VCB is demonstrated in Fig. 11.
MICROCRYOGENIC CYCTEM (MCS) OF COOLING
In order to solve the task of complete import substitution of the photodetectors designated for the placement in imaging IR equipment used for different purposes in 2011-2013 SAPPHIRE Moscow Plant OJSC was performing the research and development work. This work was devoted to the development of microcryogenic system of cooling (MCS) of integrated type with gas cryogenic refrigerator operating according to the Stirling cycle – "Сапфир-МКС" [5].
The objective of R&D work was to develop the single-block MCS for the ensuring of operating temperature of photosensitive elements 78±2 K. Due to the integrated joining of MCS with cryostats the company succeeded to obtain considerably efficient energy and mass-size characteristics of the developed systems. Main components of the developed MCS are shown in Fig. 12 and Fig. 13 and the appearance of the system is demonstrated in Fig. 14. Main parameters of MCS are specified in Table 1.
MAIN CHARACTERISTICS OF THE MODULES
ФУК 149М (Fig. 15) and ФУК 154М (Fig. 16) are the unified photodetector arrays with the format 320×240 and format 320×256 elements and range 3-5 µm. Main parameters of the modules are specified in Table 2.
ФУК 148М (Fig. 17) and ФУК 152М (Fug. 18) are the unified photodetector subarrays with the format 4×288 elements and range 8-10.5 µm functioning in two-pass mode of time delay and integration. The main parameters are given in Table 3.
ФУК 143М (Fig. 19) and ФУК 151М (Fig. 20) are the unified photodetector arrays with the format 320×256 elements and range 8-10.5 µm. The main parameters are given in Table 4.
CONTROL OF THE MODULE PARAMETERS
Measurements of photoelectric parameters (PEP) of the photoreceiving modules were accomplished on the unified measuring bench (Fig. 21). In order to automate the procedure of PEP measurements of the photoreceiving modules and record the measurement results in electronic database the specialized software (SSW) was designed. SSW interfaces in Windows operating system environment are specified in Fig. 22 and Fig. 23.
DEVELOPMENT OF BASIC TECHNOLOGIES
Since 2013 SAPPHIRE Moscow Plant OJSC has been performing Apex R&D works on the development of manufacturing technologies in respect of large-format photodetector arrays based on indium antimonide. Its purpose is to create the manufacturing technology of photodetector arrays (PDA) with the format 640×512 elements including the manufacturing technology of photosensitive arrays based on indium antimonide with the character pitch of not more than 20 µm.
When accomplishing the works the basic manufacturing technology of large-format coolable photosensitive element arrays with small pixel size and manufacturing technology of large-format coolable multiplexers with the geometry design rule of not less than 1 µm must be developed. At the same time the methods and instruments of measurements and testing will be formed for the large-format photodetector arrays based on indium antimonide. And worksites will receive instrumentation and specialized equipment in order to ensure the required technology-specific rules and product quality upon high efficiency of production.
SAPPHIRE Moscow Plant OJSC traditionally manufactures the products designated for the thermovision and thermal direction finding systems. Semiconductor IR photodetectors and photoreceiving devices based on Si, Ge, indium antimonide (InSb), cadmium-mercury-tellurium (CdHgTe) (CMT) can be marked out among them. In 2008-2010 the company was developing the second generation of batch-oriented fast-response photoreceiving modules (PRM) for the prospective imaging IR equipment [1-5]. The purpose of this development was to create industry-oriented constructions and technology of the second generation of infrared PRM assembly: PRM subarrays with the format 4×288 elements and PRM arrays with the format 320×240 and format 320×256 elements.
The work was being performed for the modernization and import substitution of PRM in imaging infrared channels for the control and observation complexes with different purposes. As a result the following PRMs of the second generation were developed:
unified PRM arrays with the format 320×240 and format 320×256 elements for the range 3-5 µm (ФУК 149М and ФУК 154М);
unified PRM subarrays with the format 4×288 elements for the range 8-10.5 µm functioning in two-pass mode of time delay and integration (ФУК 148М and ФУК 152М);
unified PRM arrays with the format 320×256 elements for the range 8-10.5 µm (ФУК 143М and ФУК 151М).
STRUCTURE OF PHOTORECEIVING MODULES
Developed PRMs are constructed on the basis of single-type scheme. It includes:
array or subarray of photosensitive elements (APSE) on the basis of photodiodes of InSb or CMT;
silicon large-scale integration (LSI) reading circuit (multiplexer) hybridized by indium microcontacts with APSE and ensuring the reading, previous amplification and multiplexing of APSE signals;
vacuum cryostatic body where APSE, silicon LSI circuit, getters and coolable diaphragm with optical filter ensuring the specified spectral sensitivity range are located;
microcryogenic system (MCS) of cooling.
PHOTODETECTOR ARRAYS BASED ON InSb
Photodetector arrays based on indium antimonide (InSb) are designated for the operation within the spectrum region of 3-5 µm. The photodetector arrays with the format 320×240 elements and format 320×256 elements with the line-frame reading organization were designed.
APSE [4] is developed on the basis of indium antimonide photodiode array with fine base region on silicon supporting template. APSE construction (Fig. 4) ensures the harmonization by thermal expansion coefficients of both elements – APSE and silicon LSI reading circuit (multiplexer). As a result, the influence of thermal mechanical stress on hybrid assembly of APSE with silicon LSI reading circuit is minimized.
Silicon LSI reading circuit (Fig. 2) is developed according to the CMOS technology with the design rules of not more than 0.8 µm [4]. LSI circuit has the necessary functional capabilities. First of all, it ensures the operation mode upon which the concurrent reading (for 4/8 yields) of complete frame with the format 320×240 elements with high sensitivity and frame frequency of not less than 200 Hz. Secondly, the reading mode of several lines has high sampling frequency (of not less than 8000 Hz). Thirdly, it determines the mode of "window" with squared shape dimensions of which are set from outside with the multiplicity by sides of 8 pixels ("window" is situated in the required place of array field).
Photodetector array is formed by the hybridization of APSE with silicon LSI reading circuit with the help of indium micropillars (Fig. 3) which are obtained via the operations of "dry" etching. Then, using the adhesive binding the photodetector array with temperature sensors is placed on the contact raster (Fig. 4) which in turn is the cryostat coolable element.
PHOTODETECTOR ARRAYS AND SUBARRAYS BASED ON CADMIUM-MERCURY-TELLURIUM
The main material for manufacturing of fast-response photodetectors with the spectral range 8-14 µm and limit characteristics of sensitivity is the solid solution of cadmium and mercury tellurides CdXHg1-XTe (CMT).
Constantly progressing the CMT manufacturing was being developed starting from the method of growth of bulk crystals from the melt at high temperature and finishing the methods of low-temperature epitaxy. Epitaxial methods are the most applicable for the growth of CMT layers with large area and creation of photodetector arrays respectively. The main methods of their obtaining are liquid-phase epitaxy (LPE) and molecular-beam epitaxy (MBE). In the Institute of Semiconductor Physics of Siberian Branch of the Russian Academy of Sciences (ISP SB RAS) the home equipment was manufactured and production-oriented technology of molecular-beam epitaxy of layers of CMT-based strategic material of modern IR equipment for the spectral range 8-14 µm was developed (ТУ 1778-003-03533808-2003).
When developing the photoreceiving module arrays and subarrays with the range 8-10.5 µm certain types of photodetectors were used.
Linear photodetector (subarray) ФП2 is the hybrid assembly on indium micropillars of photodiode subarray of CMT hetero-epitaxial structures grown by the method of molecular-beam epitaxy (HES CMT MBE) and silicon LSI circuit (multiplexer). PD is the coolable linear photodetector array with the format 288×4 elements – analog of ID TL015-XX-V3 photodetector manufactured by Sofradir Company. Assembly is designed in the ISP SB RAS [6]. Construction of the linear photodiode array is demonstrated in Fig. 5 and layout of photodiodes location in photoreceiving area is shown in Fig. 6.
Developed silicon LSI circuit (multiplexer) for ФП2 with the format 288×4 has the circuit and construction which peculiarities are: complete digital control using the parallel and series ports, deselection of any invalid cell and implementation of the function of bi-directional scanning. Hybridization of linear photodiode array with multiplexer is accomplished with the help of indium micropillars (Fig. 7).
Photodetector array ФП2М which was developed and manufactured in the ISP SB RAS represents the coolable CMT photodetector array with the format 320×256 elements with the pixel dimensions 30×30 µm [7]. Its long-wavelength cutoff is 10.5 µm. The construction of hybrid assembly of ФП2М photodetector is given in Fig. 8, and the format of receiver photosensitive field is shown in Fig. 9.
Construction diagram of photodetector array in vacuum cryostat
The construction of vacuum cryostat body (VCB) includes holder with fixed coolable elements, body with getter and cover with entrance window [1].
Simultaneously VCB holder is the tube of displacer of gas cryogenic refrigerator (GCR) which is included in the structure of MCS. The ceramic tip (contact raster) which is the mounting seat for photosensitive elements and other coolable elements of construction is secured on the edge of tube-holder. Assembly of the photodetector in VCB structure is given in Fig. 10.
The tip bond sites are connected with the bond sites of ceramic-metal base by the conductors (with diameter of 0.03 mm) of platinum (80%)-iridium (20%) alloy. Such connection ensures the optimal correlation between heat conductivity and electrical resistance.
Vacuum pumping of cryostat is performed through the copper exhaust tube inserted by the "solid" brazing (braze ПСР-72). After the pumping the exhaust tube is cut by the special wire cutter. It provides the cold (diffuse) welding of exhaust tube walls thus sealing hermetically the vacuum volume of VCB. Periodically activating the getters which are located on the inner wall of VCB maintaining or even restoration of the required vacuum in cavity is obtained if it will be necessary. Photodetector array in the structure of VCB is demonstrated in Fig. 11.
MICROCRYOGENIC CYCTEM (MCS) OF COOLING
In order to solve the task of complete import substitution of the photodetectors designated for the placement in imaging IR equipment used for different purposes in 2011-2013 SAPPHIRE Moscow Plant OJSC was performing the research and development work. This work was devoted to the development of microcryogenic system of cooling (MCS) of integrated type with gas cryogenic refrigerator operating according to the Stirling cycle – "Сапфир-МКС" [5].
The objective of R&D work was to develop the single-block MCS for the ensuring of operating temperature of photosensitive elements 78±2 K. Due to the integrated joining of MCS with cryostats the company succeeded to obtain considerably efficient energy and mass-size characteristics of the developed systems. Main components of the developed MCS are shown in Fig. 12 and Fig. 13 and the appearance of the system is demonstrated in Fig. 14. Main parameters of MCS are specified in Table 1.
MAIN CHARACTERISTICS OF THE MODULES
ФУК 149М (Fig. 15) and ФУК 154М (Fig. 16) are the unified photodetector arrays with the format 320×240 and format 320×256 elements and range 3-5 µm. Main parameters of the modules are specified in Table 2.
ФУК 148М (Fig. 17) and ФУК 152М (Fug. 18) are the unified photodetector subarrays with the format 4×288 elements and range 8-10.5 µm functioning in two-pass mode of time delay and integration. The main parameters are given in Table 3.
ФУК 143М (Fig. 19) and ФУК 151М (Fig. 20) are the unified photodetector arrays with the format 320×256 elements and range 8-10.5 µm. The main parameters are given in Table 4.
CONTROL OF THE MODULE PARAMETERS
Measurements of photoelectric parameters (PEP) of the photoreceiving modules were accomplished on the unified measuring bench (Fig. 21). In order to automate the procedure of PEP measurements of the photoreceiving modules and record the measurement results in electronic database the specialized software (SSW) was designed. SSW interfaces in Windows operating system environment are specified in Fig. 22 and Fig. 23.
DEVELOPMENT OF BASIC TECHNOLOGIES
Since 2013 SAPPHIRE Moscow Plant OJSC has been performing Apex R&D works on the development of manufacturing technologies in respect of large-format photodetector arrays based on indium antimonide. Its purpose is to create the manufacturing technology of photodetector arrays (PDA) with the format 640×512 elements including the manufacturing technology of photosensitive arrays based on indium antimonide with the character pitch of not more than 20 µm.
When accomplishing the works the basic manufacturing technology of large-format coolable photosensitive element arrays with small pixel size and manufacturing technology of large-format coolable multiplexers with the geometry design rule of not less than 1 µm must be developed. At the same time the methods and instruments of measurements and testing will be formed for the large-format photodetector arrays based on indium antimonide. And worksites will receive instrumentation and specialized equipment in order to ensure the required technology-specific rules and product quality upon high efficiency of production.
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