FR2803948A1 - Bandgap infrared radiation detector device used in thermal imager includes detector elements having linear dimensions which are each substantially smaller than the wavelength of the detected radiation - Google Patents

Abstract

Infrared detector has electrically conductive elongate members comprising photosensitive segments separated by, but contacting non-photosensitive conductive elements. Electrically isolated, parallel conductive lines are positioned immediately above detector surface, and spaced apart by less than radiation bandwidth, for enhancing capture of infrared radiation.

Description

The present invention relates generally to radiation detection devices and, in particular, to devices for detecting radiation - </ b> </ b> </ b> </ b> </ b> </ b> B> ment in the field of infrared and shorter wavelengths. </ B>

<B> Radiation detectors such as </ B> infrared detectors have long been used as thermal image formaters for night vision <B> or to make observations </ B> to < Through clouds, smoke and dust. A typical infra-red image formatter has an array of <B> detectors </ B> with a large area in which each detector corresponds to a single pixel (pixel) ) for an image. Each detector is a planar structure whose dimensions both in width and in length are greater than the wavelength of incident radiation <B> so that the detector has a suitable collecting surface <B> <B> the incident radiation. A typical detector of this type is shown in "Semiconductors <B> and Semimetals" <B> Volume 18, Mercury Cadmium Telluride, Academic Press, 1981, p. 162-163.

<B> A major limitation for the use of </ B> infrared image formatters of the usual type has been the need for the imaging device to be <B> locked in a very cold room. Cooling for such devices has often been provided by the evolution of liquid gases, such as nitrogen. But storage, piping, and handling refrigerant such as liquid nitrogen have proven to be <B> difficult, time-consuming, and expensive. </ B>

Although conventional radiation detectors can provide useful images satisfactorily, they are very limited in their operation. For a given input power of incident radiation, the level of the signal resulting from these devices is relatively small.

This is why there is a great need for an improved infrared radiation detector for the infrared zone and shorter wavelengths; such a detector must produce a signal of greater amplitude with a reduced need for the complex cooling apparatus.

A preferred embodiment of the present invention is a device for detecting incident radiation. This device comprises a support structure which comprises a dipole antenna which is mounted on this support. The length of the antenna is approximately half the wavelength of the incident radiation. This device further comprises a quantum detector element which is mounted on the support structure and which is connected to the dipole antenna. The detector element is designed so that its linear dimensions are substantially smaller than the wavelength of the incident radiation. The incident radiation is picked up by the dipole antenna and transferred to the detector element to produce an output signal indicative of the detection of radiation incident on the device.

Other embodiments of the present invention include a network of such devices and an image formatter comprising a plurality of such networks.

Other features and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention, with reference to the accompanying drawings in which: - Figure 1 is a plan view of a network devices according to the present invention for detecting incident radiation; FIG. 2 is a plan view of an alternative embodiment of a network of infrared radiation detection devices according to the present invention; - Figure 3 is a sectional view along lines III-III of the infrared radiation detection device shown in Figure 2; FIG. 4 is a perspective view of an infrared radiation image formatter in accordance with the present invention using one of the infrared radiation detector arrays shown in FIG. Figures 1 and 2; FIG. 5 is a plan view showing an infrared radiation detector of the usual type; FIG. 6 is a plan view of an infrared radiation detector according to the present invention; - Figure 7 is a sectional view along the line VII-VII of the radiation detector shown in <B> Figure 6 </ B>; FIG. 8 is a sectional view of an alternative embodiment of the present invention; Fig. 9 is a sectional view of another embodiment of the present invention employing orthogonal detector assemblies; FIG. 10 is a partial sectional plan view of the embodiment with two sets of detectors shown in FIG. 9; Fig. 11 is a sectional view of yet another embodiment of the present invention; Figure 12 is a plan view of a radiation image former using the infrared ray detector of the present invention; Fig. 13 is a perspective view of a pixel element of an infrared detector manufactured in accordance with an embodiment of the present invention; Fig. 14 is a sectional view taken along the 2x-2x lines of the detector shown in Fig. 1x; FIGS. 15A to 15K show steps of the manufacturing method of the detector shown in FIG. 13; FIG. 16 is a table illustrating the absorption of cadmium telluride and mercury radiation at room temperature for two different concentrations of mercury; Fig. 17 is an illustration of the general absorption of the infrared radiation detector shown in Fig. 13; Fig. 18 is a perspective view of a non-polarized infrared radiation detector according to the present invention; FIG. 19 is a plan view of an alternative design of an infrared detector according to the present invention; FIG. 20 is a sectional view along lines 8x-8x of the detector shown in FIG. 19; Fig. 21 is a perspective view of the infrared detector shown in Figs. 19 and 20; Figure 22 is a perspective view of an alternative embodiment of the present invention; FIGS. 23A to 23L show steps of the manufacturing method of the detector represented in FIGS. 19 to 21; FIG. 24 is the electrical diagram of a detector according to the present invention; Fig. 25 shows an infrared imaging system having an array of detectors using the detector elements according to the present invention; FIG. 26 is a perspective view of an infrared detector comprising strips of photosensitive material arranged between parallel conductors; and FIGS. 27A-27H show <B> steps of the <B> manufacturing process of the detector <B> shown <B> at FIG. 24. </ B>

<B> Referring now to FIG. 1, there is seen a network 10 of infrared (IR) radiation detectors according to the present invention. This network includes <B> a support structure 12 which provides physical support <B> and necessary electrical properties such as non-conductivity. A plurality of identical <B> detector devices 14,16,18,20,22,24,26,28 and 30 constitute a 3 x 3 matrix for the network 10. We will describe in detail < The detection device 16, which is, however, representative of the other devices in the network. </ B> <B> 10 The detection device 16 comprises a dipole antenna 36 which comprises antenna elements 36a and 36b. The antenna 36 is made from a conductive material such as that, for example, aluminum. The wave length <B> of the incident radiation is indicated by the <B> Lambda </ B> (X) symbol. <B> The length of the dipole antenna is approximately half the wavelength <B> of incident radiation. Each of the detection devices 14 to 30 has a capture area which is shown for the sensor device 22 through the oval line 38 surrounding the device 22. It can be seen that the <B> Detector devices 14 to 30 are positioned such that a substantial portion of the incident radiation is captured by the dipole antennas.

Between the antenna elements 36a and 36b there is provided a bandgap detector element 40 which is mounted on the support structure 12 and which is electrically connected to the antenna elements 36a and 36b. Blocking contacts, which will be described below, provide electrical connections between the antenna elements 36a, 36b and the detector element 40.

The support structure 12 has a thickness which is approximately equal to a quarter of the wavelength of the incident radiation. Preferred materials for structure 12 are zinc selenide or zinc sulfite.

The network 10 may serve as a pixel element in an infrared image formatter as described below with reference to FIG. 4. In such an application, the detector devices such as 16, for all the detector devices of the network 10 , are connected in common to provide a pixel signal. However it is also possible that each detector device, such as 16, each generates a pixel signal.

Referring now to Figure 2, a second configuration of the present invention is seen. This configuration is a network 50 which has a support structure 52. This structure 52 is similar to the structure 12 which has been described above. The array 50 is a 2 × 4 array including detectors 54,56,58,60,62,64,66 and 68. Each of the detecting devices, such as 56, comprises a detector element and a dipole antenna. The detector devices 54 to 68 respectively comprise the detector elements 72 to 86. Each detector element is positioned between and connected to two metal antenna elements which serve as a dipole antenna for each detector element. The antenna elements are included in the metal zones 94, 96 and 98. For example, the device 56 comprises the sensor element 74 which is connected, via blocking contacts, which will be described below, to a dipole antenna which comprises metal elements 102 and 104 which are respectively parts of the metal zones 94 and 96.

The configuration shown in FIG. 2 makes it possible to produce an output signal between the metal zones 94 and 98 because of the electrical responses provided by the detector elements 72 to 86 when receiving incident radiation. The horizontal cell spacing of the structure 50 is represented by the line 106, the vertical cell spacing through the line 108, the horizontal cell opening through the line 110 and the vertical cell opening through the line 112. For the detection of infrared radiation having a wavelength of 10 microns, the horizontal and vertical cell spacings are approximately 5 microns and the cell apertures are approximately 4.5 microns. Each of the detector elements 72 to 86 has dimensions that are approximately 0.75 x 0.25 microns. Thus, the dimensions of the detector elements are substantially less than the wavelength of the intercepted radiation. For infrared radiation with wavelengths of 5 microns, each of the linear dimensions shown above is reduced by about half, but the detector element has approximately the same dimensions.

The network 50 may similarly serve as a pixel signal source within an image formatter comprising a large number of such networks, as shown in FIG. 4. The network 50 is furthermore represented in FIG. FIG. 3. A reflective layer 116, such as metal, for example aluminum, or a multilayer dielectric, is disposed between the support structure 52 and an insulator substrate 118. The layer 116 serves as the based. A preferred composition for the substrate 118 is a silicon substrate which is a part of a chip constituting a silicon charge coupled (CCD) <B> device. which <b> <B> processes the signal produced by the network 50. </ B>

<B> The sensor element 74 is electrically connected to the dipole antenna metal elements 102 and 104 at the average of the blocking contacts. The elements 72 to 86 are preferably a telluride alloy of mercury and cadmium in which the portion of mercury and cadmium telluride <B> 86 </ b> cadmium is represented by x and the mercury part is represented by </ B> <B> (1 </ B> - <B> x). The preferred <B> telluride <B> mercury and cadmium <B> <B> alloy for detector elements 72 to 86 has the value <B> x </ B> - <B > 0.15. The network 50, with reference to FIG. 3, includes blocking contacts 120, 122, 124 and 126. The contact 120 is a layer that is on and in contact with each other. with </ B> <B> the outer surface of the detector 74. The metallic element </ B> <B> that 102 is manufactured directly on the contact 120. </ B> <B> The element 102 is connected electrically to the contact 120 but not directly connected to the detector 74. The contact 122 is disposed in a <B> <B> manner between the </ B> Detector 74 and the metal element 104. The contact 124 is located between the detector 82 and a part of the metal zone <B> <B> </ B> 96. And, analogously, the blocking contact 126 is disposed between the detector 86 and a portion of the metal zone 98. The blocking contacts <B> <B> > 120, 122, 124 and 126 comprise a <B> telluride <B> mercury and cadmium alloy for which x = 0.19. </ B>

<B> The purpose of blocking contacts 120,122,124 and 126 </ B> <B> is to avoid the diffusion of charge carriers from </ B> <B> detector elements such as 74 in the elements </ B > <B> aluminum metal such as 102 and 104. It is desirable to have a lower recombination rate <B> 500 </ B> cm / s, <B > but direct aluminum contact with the <B> <B> detector results in a recombination rate that is close to infinity. By including the blocking contacts such as 120, 122 and 124 and 126, between the detector elements and the metal dipole members, the recombination rate of the carriers is reduced to the range of 300 to 500 cm / s. The blocking contacts and the associated elements function much like high frequency coupling capacitors to provide direct current isolation of the carriers but have only a low impedance between the detector elements and the dipole antenna elements. The theory and detailed operation of a blocking contact of this type is described in "Applied Physics Letters" 45 (1), July 1, 1984, pp. 83-85 D. L. Smith, D.K. Arch, <B> P. A. Wood and Mr. Walter Scott. </ B>

The detector elements, such as 40 and 74, discussed above are direct band gap detectors. A band gap detector of this type produces an electrical signal as a result of an interaction between the incident photons and the electrons (holes) in the material. A detector element of this type is not subjected to heat exchange (phonon) noises as are bolometer detectors and the like. Thus, band gap detectors are not severely limited in performance for high (ambient) temperatures as are conventional bolometer detectors and the like.

A preferred material for the detector elements 40 and 72 to 86 is a mercury and cadmium telluride crystal. Another material may be indium antimonide. Another suitable detector element may be a semiconductor superlattice as described in the article of "Scientific American" "Solid State Superlattices" of November 1983 by Gottfried H. Dohler. Yet another detector element may be an organic material as described in Laser Focus "Organic Crystals and Polymers" on pages 59 to 64 by Antony F. Garito and Kenneth H. Singer. By using the organic matter described in the article by Garito and Singer, it is possible to obtain coherent detection of incident radiation.

Figure <B> 4 </ B> represents an image forming device 130 according to the present invention. This image forming device comprises a plurality of individual networks such as 132. The network 132 may, for example, be the same as the network 10 or network 50 described above. An infrared image is transmitted via a lens 134 to the image forming planar device 130. Each of the networks provides a pixel signal which, for the network 132, is transmitted through a line 136. There is a corresponding line for each network included in the image forming device 130. The obtaining and processing of all the pixel signals is a reproduction of the original image which has been transmitted through of the lens 134. A line 138 can provide a common ground that extends over the entire image forming device 130.

A method according to the present invention will now be described for the manufacture of the band gap detector elements. A layer of cadmium telluride is first formed by epitaxy on a substrate whose thickness is 1 to 2 microns. This layer of cadmium telluride is then exposed to mercury to form a surface layer crystal of mercury and cadmium telluride. Finally, the layer of mercury and cadmium telluride is subjected to an etching operation to form a selected array of detector elements as shown in FIGS. 1 and 2. Another method of manufacturing a mercury telluride crystal and cadmium for detectors and blocking contacts of the present application is described in "Molecular Beam Epitaxial Growth of High Quality HgTe and Hgl_zCd = Te Onto GaAs <B> (001) </ B> Substrates," Applied Physics Letters 45 (12) December 15, 1984 by JP Fauve, S. Sivananthan, M. Boukerche and J. Reno.

A major advantage of the structure of the present invention is the ability to produce an output signal for a detected infrared signal without the conventional need to cool the detector elements. A common type infrared detector element is a planar element that has a zone with dimensions that are substantially larger than the wavelength of the incident radiation. These large-area elements are needed to capture infrared input radiation.

To summarize, an embodiment of the present invention comprises a detector, a grating and an image forming device which are essentially designed to detect infrared radiation using dipole antennas which pick up the incident radiation and transfer it to a light source. bandgap detector element. The detector element has dimensions that are substantially smaller than the wavelength than incident radiation. The main advantage of the present invention is the ability to create an infrared imaging signal without the need to cool the detector elements.

Another embodiment of the present invention is an infrared radiation detector that produces an output signal when exposed to infrared radiation. Figure 5 shows a conventional infrared radiation detector 200 of the prior art. Infrared radiation having a wavelength of 8 to 12 microns is of primary interest with regard to detection because of its propagation characteristics through the atmosphere. The usual detector 200 comprises large surface detector elements such as the element 212, to capture the incident infrared radiation. Detector element 212 has conventional dimensions of length and width equal to 50 microns. The dimensions of 50 microns are well above the wavelength of 8 to 12 microns of the intercepted radiation. This configuration of large area detectors is used to capture the incident radiation on areas that correspond approximately to the size of a pixel (picture element in an image). Each of the detector elements, such as 212, produces a pixel signal and its signals are used in combination to produce an image.

Another detector 214 of infrared radiation according to the present invention is shown in FIG. 6. This detector 214 comprises a parallel periodic configuration of photoconductive or photovoltaic-type detectors elements 216,218,220,222,224,226,228 and 230. These elements must be realized in a radiation absorbing material. A preferred material for these detector elements is mercury and cadmium telluride which is designated by the formula Hg (C) (), Te, for which a selected value of x is 0.2. The detector elements 216 to 230 are connected together at their opposite ends by respective common lines 236 and 238 which are conventionally made of metal such as aluminum. In a preferred embodiment, the detector elements 216 to 230 undergo an etching operation from a single layer of mercury telluride and cadmium.

The detector elements 216 to 230 and the common lines 236 and 238 are manufactured on a substructure 240 which performs several functions. This substructure 240 provides support for the elements 216 to 230 and the lines 236, 238 and, significantly, it provides an impedance match between the free space radiation and the radiation impedance of the <B> Configuring Detector Elements 216 </ B> to <B> 230. This </ B> substructure 240 contains layers having refractive indices (n) different from that of air or free space. Substructure 240 increases the absorption of radiation by detector 214. Referring also to FIG. 7, substructure 240 includes separate layers 242 and 244. Layer 242 <B> is preferably the indium antimonide and the layer 244 is preferably cadmium telluride. The layer 242 has a refractive index n = 4 and the layer 244 has a refractive index n = 2.7, where n is 1 for the free space.

The configuration of the detector elements 216 to 230 shown in FIG. 6 comprises a pixel having a general size of 50 by 50 microns. This structure is designed to receive infrared radiation of 8 to 12 microns. Each of the detecting elements 216 to 230 has a width of about 0.5 micron and a length of about 50 microns. The preferred center-to-center line spacing period between elements 216 to 230 is 3 microns. A preferred thickness for each of the elements 216 to 230 is 0.5 micron. A preferred thickness for each of the layers 242 and 244 is on the order of 0.1 to 10 microns.

It has been determined that there is a limit criterion for the efficient operation of the present invention as shown in FIGS. 6 and 7. For normal incident radiation, this criterion has two aspects: first, the length of the the wave (X) of the incident radiation must be greater than or equal to the product of the periodic spacing (b) between the detector elements by the refractive index (n2) for the lower layer, ie the layer 244 shown in Figure 7. This is expressed as X, @ nzp. In addition, the upper layer 242 must have a refractive index (ni) greater than the refractive index (n2) of the lower layer <B> 244. </ B> This is expressed as ni> n2. When these two aspects are respected, the absorption of incident radiation for the present invention may approach $ 100. When this criterion is not fulfilled, a detector such as the detector 214 shown in FIG. 7 will be limited to a maximum absorption <B> of less than $ 50.

Although the detailed theoretical operation of the present invention is not yet completely understood, it appears that the incident radiation, which is not directly absorbed by the detector elements 216 to 230, is essentially trapped in the layer 242 because of the values. different refractive index between the layer 242 and the layer 244 on the one hand and between the layer 242 and free space on the other.

It is likely that the incident radiation is diffracted by the detector elements 216 to 230 so as to change its direction of propagation away from the normal incidence path. The trapped radiation is absorbed when it finally hits the detector elements 216 to 230 after possibly many reflections. It appears that the radiation which is able to escape from the layer 242 by returning to the free space through the plane of the detector elements 216 to 230 is suppressed by the incoming incident radiation, which contributes to the complete absorption of the radiation. inci dent.

All detector elements 216 to 230 are connected in parallel between lines 236 and 238. Line 236 is connected via two conductors 246 to a terminal of a DC power source or a battery 248. B> The line 238 is connected via a conductor 250 to a terminal 252. A resistor 254 is connected between the terminal 252 and a terminal 256. The other terminal 248 of the battery is connected to the terminal 256. The battery 248 applies a bias on the sensor elements 216 to 230 and the resistor 254 serves as charge <B> in series. When infrared radiation is sensed by the detector 214, electrons found in the detector elements 216 to 230 are driven in bands </ B>. at higher energy which change the current intensity produced by the battery 248. This causes variations in the current flowing through the resistor 254, which <B> alters the voltage between the terminals 252 and 256. In this manner, the detector 214 provides a pixel signal on the terminals 252 and 256. A series of detectors, such as the detector 214, provides a complete image by generating a signal for each pixel. </ B>

<B> The detector according to the present invention has a better response because of the radiation power density captured in the sensing material compared to a conventional infrared detector. For example, the detector 212 of FIG. 5 and the detector 214 of FIG. 6 have the same overall dimensions in the plane. The detector 212 has an active surface area of 2500 square microns with a typical thickness of 10 microns, but the detector 214 has an active area of only about 425 square microns with a typical thickness of 0.5 microns. With equal intensity of incident radiation, the detector 214 will have a power density approximately 120 times greater in the sensing elements, which provides a significant increase in performance. Since the widths of the detector elements 214 become smaller, the increase in power density becomes even greater. The detector of the present invention thus provides a significant performance advantage over conventional large area detectors. The substructure 240 serves to provide impedance matching between the free-space radiation impedance and the beam impedance of the detector elements 216 to 230. A basic measure of the performance of a detector of Radiation is the absorption percentage for incident radiation. Without the substructure 240, the elements 216 to 230 have a radiation absorption of less than $ 5, but if the substructure 240, which satisfies the above criteria, is added, the absorption is increased to arrive at a value greater than $ 80 as shown by computer simulations.

The different detectors described for this embodiment for the present invention employ parallel detection strips, but, generally, recurring elements of all shapes can be used provided that the spacing between the elements is less than or equal to the wavelength of the incident radiation.

Yet another embodiment of the invention of the present invention is shown in Fig. 8. A detector 260 is similar to the detector 214 shown in Fig. 6 and 7 but with the addition of a higher structure so providing additional impedance matching between the detector elements and the impedance of the free space. The detector 260 has a set of parallel detector elements 262, 264, 266, 268, 272, 272, 274 and 276 which are the same as the detector elements 216 to 230 of the detector 214. The detector 260 has a substructure 280 comprising layers 282 and 284 which correspond to the layers 242 and 244. 244 of the detector 214. The detector 260 also comprises an upper structure 286 comprising layers 288 and 290. The layer 288 is similar to the layer 242 of the detector 214 and the layer 290 is similar to the layer <B> 244 </ B The upper structure 286 functions as the substructure 240 to improve the impedance matching between the elements 262 to 276 and the radiation impedance of the free space.

FIGS. 9 and 10 show another embodiment of the present invention, namely a detector 296. This detector 296 comprises sets of detector elements 298 and 300 each of which is the same and is electrically connected to the same. detector elements 214 and shown in FIG. 6, but the detector elements of the assembly 298 are arranged perpendicularly to the detector elements of the assembly 300. The signals detected from the two sets can be combined with each other. born electrically. The detector 296 includes a substructure 302, an upper structure 304 and an intermediate structure 306. The substructure 302 comprises layers 308 and 310 and the upper structure 304 comprises layers 312 and 314. The substructure 302 corresponds to to the substructure 280 and the upper structure 304 corresponds to the upper structure 286. The intermediate structure 306 comprises layers 316 and 318 each of which is preferably of a material such that cadmium telluride having a thickness of approximately 0, 1 to 10 microns. The detector assembly 298 is in the layer 316 and the detector assembly 300 is in the layer 318. The two sets of detector elements 298 and 310 are orthogonally oriented to sense orthogonal polarizations of the incoming radiation. The structure shown in Figure 6 captures only one polarization. A sectional and plan view of the detector 296 is shown in FIG. 10 with the upper <B> structure 304 removed and the detectors of the assembly 300 shown as broken lines.

Fig. 11 shows a detector 320 which <B> is yet another embodiment of the </ B> present invention. This detector comprises a substructure 322 which is, for example, a dielectric layer or plate 330 preferably made of cadmium telluride and having a thickness of 0.1 to 10 microns. On the surface of the substructure 322 a plurality of parallel detector elements such as 324,326 <B> and 328 are arranged. These elements are arranged and connected in a manner </ B> <B> as presented </ B> to <B> Figure 6 for the elements 216 </ B> to 230. The elements 324 to 328 are made of the same material as the elements 216 to 230. On the underside of the plate 330 is provided a layer 332 comprising a metal such as aluminum. The layer 232 has a thickness preferably equal to 0.5 micron. The substructure 322 comprises the dielectric plate 330 and the metal layer 332.

The dielectric plate has a thickness which preferably depends on the wavelength of the incident radiation. The preferred thickness is an odd multiple of the quarter-wavelength of the received radiation. For a radiation wavelength of 12 microns, a thickness of up to 10 microns is acceptable. Computer simulations show that the detector 320, with the dimensions shown, will have a radiation absorption of almost $ 100.

The detector 320 operates in the same manner as the detector 214 described above. The metal layer 332 provides the reflective bottom face as the interface between layers 242 and 244 provides a reflective surface. <B> An infrared imaging device 330 </ B> according to the present invention is shown in FIG. 12. This image formatter 330 comprises an array of detectors such as the detector 332. Each of the detectors, such as 332, produces a pixel signal and <B> all of the pixel signals form an image. Each of the detectors of the imaging device 330 <B> has a separate output line for that pixel signal of the detector. The imaging device 330 may use, with respect to the detectors 332, any of the detectors described herein, including the detectors 214,216,296 or 320 described herein. -above.

Other embodiments of the present invention are shown in Figures 13 to 27A-27H. A 20x infrared detector manufactured in accordance with the present invention is shown in perspective on FIG. 13 and in section in FIG. 14. These views are not necessarily to scale. A detailed description of the manufacturing steps of the 20x detector according to the present invention is provided in Figs. 16A to 16K. The 20x detector comprises a substrate 22x which is preferably made sapphire but which optionally can be made of cadmium telluride or </ B> B> silicon. The preferred thickness of the substrate 22x is <B> approximately 2 mm. On the upper face of the 22 × substrate there is provided a 24x reflective plane which is preferably an aluminum layer having a thickness of approximately 500 to 1000 angstroms. A 23x epoxy bond layer connects the 24x reflex plane to the 22x substrate. </ B>

On the surface of the plane 24x, there is provided a rectangular array of insulating blocks represented by the blocks 26Ax to 26Ex. These blocks are preferably made of cadmium telluride and have lateral dimensions <B> approximately equal to 4 x 1 micron and have a thickness approximately equal to 0.3 microns. The center-to-center space of these blocks is approximate - 8 microns. All dimensions determined for the 20x detector are based on a pre-design <b> <b> as well as an optimal response on a wave length band </ B> <B> <B> 12 microns for infrared radiation </ B> <B> incident. The dimensions would be proportionally modified for a different wavelength. </ B>

<B> Immediately above the insulation blocks </ B> 26Ax <B> to </ B> 26Ex <B> is a set of segments that are photo-sensitive to infrared radiation in the range from 8 to <B> 12 microns. These are photosensitive segments 28Ax <B> to <28Ex <B> that have essentially the same lateral dimensions - </ B> <B> segments </ B> 26Ax <B > to </ B> 26Ex <B> and a thickness of ap - </ B> <B> approximately 0.5 micron. These segments include </ B> telluride <B> of mercury and cadmium </ B> (MCT) <B> with a ratio <x of approximately 0.15, which corresponds to </ b> / B> pond at an operating temperature of 300 K. The telluride <B> of mercury and cadmium is specified by </ B> <B> fractional parts among which the fractional fraction </ B> <B> cadmium is represented <B> by the ratio </ B> <B> of alloy x and the fractional part of mercury is </ B> represented by (1 - x).

The link between the blocks 26Ax to 26Ex and the corresponding segments 28Ax to 28Ex is constituted by a blocking junction which avoids the transfer of all the majority and minority carriers. </ B> > <B> This junction can be <B> performed <B> by providing a short </ B> <B> transition between photosensitive segments and </ B> non-photosensitive segments.

Non-photosensitive segments 30Ax to 30Fx which constitute a bridge are arranged immediately above the photosensitive segments 28Ax to 28Ex. The 30Ax to 30Fx bridging segments comprise mercury and cadmium telluride in which the x alloy ratio is greater than or equal to 0.2. With this ratio x, the segments 30Ax and 30Fx are not photosensitive to infrared radiation in the wavelength band of 8 to 12 microns for an operating temperature of about 300 K. Each of the segments 30Ax to 30Fx is a bridge between a pair of segments 28Ax to 28Ex. For example, the 30Bx segment bridges the 28Ax and 28Bx segments. For each of the 30Ax to 30Fx segments, the preferred length is about 6 microns, a preferred width is 1 micron and a preferred thickness is 0.25 microns. The interval between the 30Ax to 30Fx segments is approximately 2 microns.

Each of the segments 30Ax to 30Fx is in contact with two of the segments 28Ax to 28Ex. The junction between these segments is a selective blocking junction, a heterojunction. This junction blocks the minority carriers but allows the majority carriers to cross. In the preferred embodiment, the minority carriers are P-type holes and the majority carriers are electrons. For this reason, the electrons pass freely through the junction while the P-type holes are blocked. One method of making this type of junction is to graduate the transition of the alloy ratio between the two segments over a distance of approximately one thousand angstroms. Other techniques are well known to those skilled in the art.

The combination of blocks 26Ax to 26Ex, segments 28Ax to 28Ex and segments 30Ax to 30Fx comprises a structure 32x which is repeated in the form of identical structures 34x, 36x, 38x and 40x. Each of these structures is an elongated, segmented and electrically conductive element. The 32x to 40x structures are parallel and are spaced apart by a distance that is less than <B> the wavelength of the incident infrared radiation </ B> considered. <B> A preferred central line spacing </ B> to a <B> central line is 8 microns.

The combination of the 30Ax 30Fx and 28Ax 28 Ex segments includes an elongated, segmented and electrically conductive element which serves to trap incident infrared radiation and to transfer the radiated energy. <B> <B> photosensitive segments </ B> 28Ax <B> to </ B> 28Ex, <B> a detection signal is generated and transmitted electrically along the element. The plurality of detection signals generated by the multiple photosensitive segments 28Ax through 28Ex are added along the segmented and electrically conductive element. </ B>

<B> The photosensitive segments <B> 28Ax to 28Ex <B> and the corresponding </ B> segments in the other structures are preferably separated from each other, in the embodiment shown, by a distance less than <B> wavelength of incident radiation. Reflective plate <B> 24x is spaced from the photosensitive segment plate </ B> 28Ax to 28Ex <B> by a distance less than </ b> the wavelength incident radiation and the reflector plate 24x is spaced apart from the photosensitive elements by a distance equal to a quarter of a wavelength.

The segment 30Ax and the corresponding segments in the 34x, 36x, 38x and 40x structures are connected to a conductive element 42x which comprises the same material <B> as the segment </ B> 30Ax <B> and which is </ B > preferably <B> an extension - </ B> of the latter. A similar conductive element 44x <B> is connected to the </ B> segment_30Fx <B> and corresponding segments </ B> of the 34x, 36x, 38x and 40x structures. A conductive lead member 46x, preferably an insulator layer, is formed on the surface of the member 42x to provide electrical contact to the member 42x. A similar conductive element 48x is provided on the element 44x. The conductive elements 46x and 48x are connected to a <B> polarization voltage, <B> as described in detail below, and are used to capture the detection signals that are generated in the 32x structures. at 40x.

<B> When the material constituting the elements 42x </ B> and 44x is of the n type, indium is the preferred material <B> for the conductive elements 46x and 48x. But if the constituent material of the elements 42x and 44x is of the type p, it is gold which is the preferred material for the elements. 46x and 48x drivers. </ B>

<B> 50x, 52x, 54x, 56x, 58x <B> and 60x </ B> <B> conductors extend transversely from the 32x to 40x structures and are immediately above the respective <B> segments </ B> 30Ax, 30Bx, 30Cx, 30Dx, 30Ex <B> and </ B> 30Fx <B> and </ B> <B> of the corresponding segments in the structu- </ B> res 34x to 40x. Each of the 50x to 60x conductors is electrically isolated from any other circuit element found in the 20x detector. These conductors are preferably aluminum and have a width of 2 microns and a thickness of 0.1 microns. The spacing from <B> center </ B> to <B> center is approximately 8 microns. These </ B> conductors extend over the entire network constituted by <B> by a plurality of detectors 20x. These conductors operate to couple more of the energy of the incident infrared radiation into the photosensitive segments such as 28Ax to 28Ex.

The 20x detector of Figure 13 is shown <B> with large open spaces between the blocks and segments of the different structures. However, these </ B> open spaces shown in this Figure 13 below the plane of the conductors 50x to 60x are filled with a non-conductive material such as sulfide of </ B> </ b>. B> zinc. This filler material has not been shown in FIG. 13 to facilitate the view of the 20x detector structure. This filler material is shown in Figures 15D-15K. Referring to FIG. 13, during operation, the incident infrared radiation represented by the arrows is received by the detector 20x. The infrared radiation falls on the upper surface of the detector 20x as shown in FIG. 13. The incident infrared radiation is essentially captured by the structural combination of the 24x reflector plate, non-photosensitive segments and photosensitive segments, with the 50x conductors to 60x. The infrared energy is transferred to the photosensitive elements 28Ax to 28Ex and the corresponding elements, the structure as a whole providing a significant impedance matching to that of the incident field. The purpose of the non-photosensitive elements 30Ax to 30Fx is to increase the impedance match and provide a direct current path for the DC current to extract the photoelectrically generated signal current. The detection signal of the photoelectric current produced by the photosensitive elements is extracted by the electrode conducting elements 46 and 48 which are biased by a DC voltage.

The 50x to 60x conductors may extend over the top of the 20x detector and are preferably spaced from each other by 8 microns. The 50x to 60x conductors can extend over a 20x detector array and serve to increase the capture of incident infrared radiation. Without the 50x to 60x drivers, the 20x sensor captures approximately $ 50 of the incident infrared radiation on the 8 to 12 micron wavelength band. But if one incorporates the 50x conductors at 60x, the capture of the incident radiation is increased to about 70% for the band concerned. 50x to 60x leads reduce sensitivity to 20x detector poralisation. These percentages were determined by computer simulations for the described structure.

The detector 20x is further shown in section in FIG. 14. This sectional view is taken along the 2x-2x lines of FIG. 13.

The detector 20x shown in Figures 13 and 14 may comprise a single pixel within an image. A two-dimensional zone of detectors 20x, as shown in FIG. 25, can be used to produce an infrared image.

A sequence of steps according to the present invention for the manufacture of the detector 20x is shown in Figs. 15A to 15K. As shown in FIG. 15A, there is provided a substrate 70x which is preferably of cadmium and zinc telluride having a crystal orientation of 2 degrees to the axis (100). The substrate 70x has a thickness of about 2 millimeters. On the surface of the substrate 70x, a layer 72x of mercury and cadmium telluride having an alloy ratio x = 0.2 and a thickness of approximately 2.0 microns is produced by drawing. On the surface of the layer 72x, a layer 74x of mercury and cadmium telluride having an alloy ratio x = 0.15 with a thickness of about 0.5 micron is produced by drawing. On the surface of the layer 74x, a layer 76x of cadmium telluride is provided. The layer 76x does not include mercury and therefore has an alloy ratio x = 1.0. The layer 76x has a preferred minimum thickness of 1.0 micron. Each of these layers 72x, 74x and 76x is preferably formed by an epitaxial process using a metal-organic chemical vapor deposition epitaxy (MOCVD) or epitaxy method. by molecular beam (MBE). <B> If we refer to <B> in Figure 15B, we see a </ B> <B> precision thinning step of the </ B> cdTe <B> 76x layer either by wet etching using diluted brominated methanol <B> or by free radical plasma etching </ B> <B> free methyl. The preferred <B> approach <B> is the plasma dry attack. The final thickness is <B> determined by <B> <B> <B> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> infrared interference spectroscopy </ B> <B> (0.8-2.5 microns). The plasma dry attack operation can be carried out using a secondary residual-incandescent reactor. In such a reactor, there is a <B> discharge of </ B> into a fluorine source gas. </ B> <B> This produces a residual incandescent current. Methane is injected into the residual incandescent stream to produce methyl radicals that attack the telluride <B> <BR> <BR> <BR> <BR> <BR> of cadmium. The facility to <b> <b> perform this process is produced by Plasma Company </ B> Quest, Inc. <B> of Richardson, Texas. </ B>

<B> If we refer to <B> in Figure 15C, we apply a <B> photoresist <B> to the surface of the 76x layer and, by </ B> <B> use of photolithography techniques, the 76x and 74x layers are attacked to produce 76Ax <B> and 76Bx <B> isolator blocks, and photosensitive segments </ B> 74Ax <B> and </ B> 74Bx. <B> A <B> selected photoresist <B> is AZ5214 <B> and a selected <B> attack reagent is a free radical </ B> <B> as noted above. The 76Ax <B> and </ B> 76Bx <B> insulation blocks correspond to the insulation blocks </ B> 26Ax <B> to 26Ex <B> and </ B> <B> 13. Similarly, the photosensitive segments 74Ax <B> and </ B> 74bx <B> correspond to the </ B> <B> photosensitive segments. </ B> 28Ax to 28ex <B> shown on the </ B> figure 13.

<B> Referring now to <B> Figure 15D, <b> <B> applies a filler material 78x consisting of zinc sulfide and which fills the open areas between </ B> <B> attacked stacks including blocks 76Ax to 76Bx <B> and segments </ B> 74Ax <B> and </ B> 74Dx. <B> The 78x filler material extends to the surface of 76Ax and 76Bx blocks. The filler material 78x is preferably applied by a gas phase deposition method by electronic bombing.

Referring now to Fig. 15E, the reflective plane 24x is applied by gaseous deposition of aluminum by electron bombardment on the top face of the filler material 78x and the surface of the blocks 76Ax and 76Bx. The aluminum layer comprising the plate 24x preferably has a thickness of about 500 to 1000 angstroms. This plane is reflective for infrared radiation.

Referring to Fig. 15F, an adhesive layer 80x, which is preferably an epoxy resin such as Epoxy Technology 301-2, is applied to the surface of the 24x plane. The 80x layer is about 0.5 micron thick. The epoxy layer 80x corresponds to the layer 23x shown in FIG. 13. An upper layer which is the substrate 22x shown in FIG. 13 is applied to the epoxy adhesive layer 80x so that the substrate 22x, which constitutes an upper layer is connected to the structure comprising the reflector plane 24x, the filler material 78x, the blocks 76Ax and 76Bx, the segments 74Ax and 74Bx, the layer 72x and the substrate 70x.

Referring now to Fig. 15G, another step of the manufacturing operation for producing the detector 20x is seen. In the step shown in Fig. 15G, the substrate 70x has been removed, preferably by an etching process. The orientation of the device has been changed by a rotation of 180. This is done in FIG. 15G in order to make the description of the process easier to understand and to position the resulting element in the same orientation as the detector 20x shown in FIG. 13. The substrate 70x can be eliminated by n '. any of many techniques including lapping or the usual attack. A preferred technique is etching using a technique described in an article entitled "Selective Etching of CdTe and ZnCdTe Substrate from HgCdTe Epilayers" by GM Metze, DL Spears and NP Walsh of the Lincoln Laboratory, MIT, published in the Proceedings of the "Meeting of the IRIS Specialty Group on Infra Red Detectors", August 6 to 8, 1985, Volume 2, pages 123 to 132, dated August 7, 1985.

In FIG. 15H, the layer 72x is etched by photolithographic methods to form 72Ax, 72Bx and 72Cx bridge segments. A preferred photoresist is AZ5214 and a preferred etching reagent is free radicals of methyl as indicated above. These segments correspond to the non-photosensitive segments 30Ax to 30Fx shown in FIG. 13.

Referring now to FIG. 151, there is shown the step of depositing 82x, 84x and 86x aluminum conductors which correspond to the 50x to 60x conductors. This is done using photolithography as by gas phase deposition of aluminum by electron bombardment. Indium conductors for the conductor elements 46x and 48x are formed in a subsequent step.

Referring now to FIG. 15J, passivation layer 88x is applied to the surface of conductors 82x at 86x, the free area of segments 72Ax, 72Bx and 72Cx as well as the free surfaces of segments 74Ax and 74Bx. Thus the entire free surface of the device is covered by the passivation layer 88x. This layer 88x is preferably zinc sulfide having a thickness of about 0.1 microns. Referring now to FIG. 15K, there is shown symbolically the step of attaching terminals to appropriate surface conductors of the device followed by encapsulation of the device. This step represents the known terminal setting and encapsulation operations for the semiconductor devices.

The infrared absorption characteristics for the photosensitive and non-photosensitive segments shown in Figs. 13 to 15 are shown in Fig. 16. The term "photosensitive" refers to the infrared band concerned. The table in FIG. 16 represents the infrared radiation absorption characteristic for mercury telluride and cadmium telluride (TCM). Curve 87x represents the sorption characteristic for MCT having an alloy ratio of about x = 0.2. It should be noted that with this ratio, MCT is absorbent for infrared radiation essentially for the range of 4 to 8 microns. Curve 89x represents the absorption of MCT having a factor x = 0.15. It should be noted that the MCT having this ratio has a high absorption for the range of 8 to 12 microns. Thus, MCT having a ratio x = 0.2 is substantially non-photosensitive in the range of 8 to 12 microns. These absorption curves are those of the MCT at room temperature. Curve 87x corresponds to bridge segments 30Ax to 30Fx. Curve 89x represents the photosensitivity characteristic of segments 28Ax to 28Ex.

With reference to FIG. 17, an infrared absorption curve 91x is shown which represents the overall infrared absorption of the device 20x shown in FIGS. 13 and 14. As can be seen, this device has a very high percentage of absorption for the 8 to 12 micron range. The absorption reaches nearly $ 100 for a wavelength in the band concerned. It is precisely this range of wavelengths which presents the main interest for the formation of thermal images. This absorption curve was determined for the 20x detector by computer modeling.

Another embodiment of the detector is the 90x radiation detector shown in FIG. 18. This 90x detector is a non-polarized embodiment of the detector 20x shown in FIG. 13. The 90x detector has the same basic structures 22x, 23x and 24x. However, the 50x to 60x elongated conductors are replaced by additional elongated structures to render the 90x detector polarization insensitive. The 90x detector captures both horizontally and vertically polarized infrared radiation. The 90x detector has a plurality of elongate structures 92x, 93x, 94x, 95x and 96x. The structure 92x will be described in detail as an example of the other structures. This 92x structure includes rectangular insulating blocks 98Ax, 98Bx, 98Cx, 98Dx and 98Ex. These correspond to blocks 26Ax to 26Ex shown in FIG. 13.

On the surface of blocks 98Ax to 98Ex, 100Ax, 100Bx, 100Cx, 100Dx and 100Ex photosensitive segments are provided which are similarly shaped. They correspond to the photosensitive segments 28Ax to 28Ex shown in FIG. 13. The 90x detector further comprises X-shaped non-photosensitive members 10x, 102x, 103x and 104x. They are made of the same material as the 30Ax segments. at 30Ex shown in Figure 13. The segment 101x bridges the segments 100Ax and 100Bx. The segments 102x, 103x and 104x similarly bridge corresponding photoconductive segments. In a direction transverse to structures 92x to 96x, structures 105x, 106x, 107x and 108x were provided. Structure 108x will be described in detail as an example of the other parallel structures 105x to 107x. Structure 108x includes isolating blocks 110Ax, 110Bx, 110Cx, 110Dx, 110Ex and 110Fx. These latter correspond in terms of dimensions and material to blocks 26Ax to 26Ex shown in FIG. 13.

On the surface of blocks 110Ax to 110Fx, there are corresponding photosensitive segments 112Ax, 112Bx, 112Cx, 112Dx, 112Ex and 112Fx. These correspond in terms of dimensions and material to the photosensitive segments 28Ax to 28Ex shown in FIG. 13.

The non-photosensitive 101x segment bridges analogously the photosensitive segments 112Ax and 112Bx. The corresponding bridge segments 113x, 114x, 115x and 116x of the structure 108x bridge the corresponding elements 112Bx to 112Fx.

The manufacture of the 90x detector is substantially the same as that described for the 20x detector but with masks suitably modified to provide the additional elements and modified shapes.

The detector 90x further includes conductive elements 114x and 116x. The element 114x is made of the same material as the bridge structures such as 101x to 104x and is an extension of these elements on the edge of the detector 90x. On the surface of the element 114x, there is provided a connection terminal 115x which is preferably an indium contact. Conductive element 116x corresponds to element 114x and has a similar conductive terminal 117x on its surface. The elements 114x and 116x are supported by respective insulators 118x and 119x. A DC bias for the 90x detector is applied between the <B> 115x and 117x terminals and the sensed signal is similarly taken from these terminals.

<B> The 90x detector works the same way as described above for the 20x detector, but it has increased performance because of the radiation capture - </ b> B> <B> incident incident polarized in a transverse direction. </ B> This eliminates the need for the 50x to 60x conductors shown in Figure 13.

Figures 19, 20 and 21 show yet another 200x radiation detector manufactured in accordance with the present invention. This 200x detector is similarly designed to capture infra <B> red radiation in the wavelength range of 8 </ B> to <B> 12 mi - </ B> crons. The elements of the detector 200x are fabricated on a dielectric substrate 212x which is, for example, cadmium telluride, exactly as for the substrate 22x shown in FIG. a plurality of elongate, segmented and electrically conductive elements 214x, 216x, 218x, 220x, 222x and 224x are provided on the surface <B> of the substrate 212x. Representative dimensions for each of these elements are 1.0 micron width, 0.5 micron thickness, and 50 mi <B> cron length. </ B>

At the opposite ends of the elements 214x to 220x, there are provided electrically conductive terminal elements 226x and 228x which connect the ends of the elements 214x to 224x in parallel. The elements 226x and 228x are preferably made of the same material as the non-photosensitive but conductive segments such as the <B> 30Ax <B> 30Fx <B <30Ax <B> elements. FIG. 13. Each of the 226x and 228x elements preferably has a width of about 2 to 5 microns and a thickness of about 0.5 microns. The element 226x has a conductive terminal 227x, preferably an indium layer on its surface. The element 228x similarly has a conductive terminal 229x on its surface.

Each of the elements 214x to 224x has a plurality of segments along its length. A preferred material for these elongated elements is mercury telluride and cadmium. The photosensitivity characteristic of this material is determined by the ratios between mercury and cadmium elements. Each of 214x to 224x includes mercury and cadmium telluride, but alternating segments have different alloy ratios that alter the photosensitive nature of the segments relative to the wavelength of the incident radiation. For this embodiment, each photosensitive segment has a length of about 3 microns and each of the non-photosensitive segments is approximately 5 microns in length.

Element 224x is described in detail as an example of all elements 214x to 224x. This element 224x comprises segments 224Ax to 224Kx connected in series. The segment 224Ax is electrically connected to the conductive element 226x. Similarly, the segment 224Kx is connected to the electrically conductive element 228x.

Each of the elements 214x to 224x is made of mercury and cadmium telluride, but the linkage ratio of the segments is different. For operation at ambient temperature, the segments 224Ax, 224Cx, 224Ex, 224Gx and 2241x have a ratio x greater than or preferably equal to 0.2, which is sufficiently high to render this material transparent to infrared radiation at room temperature. above the band of wavelengths concerned, that is to say 8 to 12 microns. For the segments 224Hx, 224Dx, 224Fx, 224Hx and 224Jx the value of the alloy ratio x is approximately equal to 0.15 in order to make this material absorbent, ie photosensitive, for the length band 8 to 12 micron wave. As a result, the segments 224Bx, 224Dx, 224Fx, 224Hx and 224Jx are photosensitive while the other segments are not photosensitive for the wavelength band of interest. It can thus be seen that the segments 224Ax, 224Cx, 224Ex, 224Gx, 224Ix and 224Kx correspond to the non-photoconductive segments 30Ax to 30Fx shown in FIG. 13. Similarly, the composition and operation of the segments 224Bx, 224Dx, 224Fx , 224Hx and 224Jx correspond to those of the photosensitive segments 28Ax to 28Ex shown in Figure 13.

The detector 200x is shown in section in FIG. 20. A reflective plane of the layer 236x, preferably an aluminum layer having a thickness of about 500 to 1000 angstroms, is shifted from the elements 214x to 224x a distance. less than 0.5 micron which is less than the wavelength of the radiation concerned. A 235x layer of zinc sulfide is placed between the layer 236x and the substrate 212x. The preferred value of the offset distance is one quarter of the optical wavelength for the radiation at the center of the band concerned. The radiation wavelength inside the detector material is essentially shorter in the free space.

An additional substrate section 238x may be provided below the reflective layer 236x to improve the cohesion of the structure. The substrate section 238x is attached to the reflective layer 235x by an epoxy layer 237x. The constituent material of the substrate 238x may be the same as that of the substrate 212x.

The reflective plane in the form of layer 236x may, in a variant, make a dielectric discontinuity between the substrates 212x and 238x, this <B> discontinuity serving </ B> to <B> reflect the infra-</ B> red radiation. Such discontinuity may be provided by adjacent substrate layers having different dielectric indices. In such a configuration, the 236x aluminum layer would not be needed.

Referring to Figs. 19 to 21, the preferred thickness for elements 214x to 224x is 0.5 microns. A preferred thickness for the lower substrate 238x is 2 millimeters.

The operation of the detector 200x will now be described with reference to Figs. 19 to 21. Infrared radiation is directed through a lens (shown in Fig. 25) on the surface of the detector 200x. The object of the present invention is to capture a very high percentage of the incident radiation and to transfer the energy of this radiation to the photosensitive detector elements. These include the photosensitive segments such as the segments 224Bx, 224Dx, 224Fx, 224Hx and 224Jx which produce a detection signal which is proportional to the amplitude of the incident radiation. Infrared radiation, in the preferred example, is captured by the combination of the structure comprising the reflective layer 236x and the structure of the elongated elements 214x to 224x which include both non-photosensitive segments and photosensitive segments.

The photosensitive segments 28Ax to 28Ex (FIG. 13) and the segments 224Bx, 224Dx, 224Fx, 224Hx and 224Jx (FIG. 18) have the following physical properties: 1. Non-zero conductivity, that is, they are conductors for direct current.

2. The conductivity for infrared radiation is determined and different from zero. 3. They are dielectric with a preferential index equal to n = 3.6 to 3.8.

<B> 4. The alloy ratio x is preferably <0.15 at room temperature. </ B>

<B> 5. Non-zero absorption of infra-red </ B> radiation.

The non-photosensitive segments 30Ax to 30Fx (FIG. 13) and the segments 224Ax, 224Cx, 224Ex, 224Gx, 224Ix and 224Kx (FIG. 18) have the following physical properties: 1. Non-zero conductivity, that is to say they are conductive for direct current.

<B> 2. Conductivity for infra - </ B> red radiation is zero.

3. The alloy ratio x is preferably greater than 0.2 at room temperature.

4. They are dielectric and have a preferred n-3.6 constant.

5. No infrared absorption.

Fig. 22 illustrates yet another embodiment of the invention manufactured in accordance with the present invention. A 300x detector has a structure as shown in FIG. 21 with the addition of conductive lines 302x, 304x, 306x and 308x. The other structural elements are the same as those shown in FIG. 21 and are indicated by the same reference numerals. The conductive lines 302x, 304x, 306x and 308x are preferably aluminum and extend transversely over the elongated elements 214x to 224x. The 302x to 308x aluminum conductor lines are each independent and are not electrically connected to each other or to another element of the 300x detector. These lines 302x to 308x have the function of improving the radiation uptake by the detector 300x exactly like the conductors 50x to 60x shown in FIG. 13.

For the 200x and 300x detectors, a DC bias signal is applied between the electrically conductive elements 226x and 228x. The photosensitive detector segments provide charge carriers and therefore modify the impedance when receiving infra-red radiation energy. These impedance changes modify the applied bias signal. The amplitude variations of the polarization signal constitute the detected signal.

For the detector 300x, the capture structure also includes all the conductive lines which comprise the lines 302x to 308x. This structural combination can capture a very high percentage of the overall incident radiation in a given band. FIG. 17 also shows the capture curve of such a radiation for the 300x detector, as obtained by theoretical modeling. The captured percentage is close to $ 100 for the wavelength chosen for the design of the device.

The method of manufacturing the 200x and 300x detectors in accordance with the present invention is shown in Figs. 23A-23L. Referring to Fig. 23A, there is shown a substrate 250x which is preferably of cadmium telluride and has a thickness of 2 mm. A mercury and cadmium telluride layer 213x is formed by drawing using the MOVCD or MBE method cited above on the surface of the 250x substrate. A layer 212x of cadmium telluride is formed by drawing on the surface of the layer 213x. The layer 213x preferably has a thickness of 2 microns and the layer 212x preferably a thickness of 0.5 micron.

Referring now to Fig. 23, the cadmium telluride layer 212x is thinned by a process selected from the many known processes. The material constituting the layer 212x can be thinned by wet etching or dry etching. The desired final thickness of the 212x layer is approximately 0.3 micron. This can be measured by near infrared interference spectroscopy (0.8 to 2.5 microns). The layer 212x is thinned accurately to adjust the distance between the photosensitive elements and the reflective plane.

Referring now to FIG. 23C, an insulating layer 235x of zinc sulfide is deposited on the surface of the thinned 212x layer of cadmium telluride. An aluminum layer 236x, which serves as a reflective mirror, is deposited on the surface of the 235x layer of zinc sulfide. The preferred thickness for the 235x zinc sulphide layer is 0.1 micron and the preferred thickness of the 236x aluminum layer is 500 to 1000 angstroms. The zinc sulfide layer serves as additional insulator to prevent leakage of any currents from the photosensitive segments and conductors to the substrate. If the 212x layer of cadmium telluride has a sufficiently pure quality, it is a very good insulator and the additional layer 235x zinc sulfide is not necessary.

Referring to Fig. 23D, an upper structure, which includes the substrate 238x is attached by means of an epoxy layer 237x to the surface of the aluminum layer 236x.

Referring now to FIG. 23E, the 250x substrate is removed from the overall structure by a process selected from the many known processes. This is the same as described above for the removal of the substrate 70x with reference to Figures 15F and 15G. As indicated, the layer 70x can be removed by mechanical break-in or etching using the processes described. In FIG. 23E, the structure has been rotated 180 degrees to improve the description of the following steps and this structure corresponds to the orientation of the described detectors 200x and 300x.

In FIG. 23E, the 213x layer is thinned to a desired thickness of about 0.5 microns. The material can be removed using a process selected from many known processes including mechanical lapping or wet or dry etching. A preferred etching reagent is dilute brominated methanol. Dry etching can be performed as described above for layer 76x in FIG. 15B. The thickness of the 213x layer can be measured using infrared interference spectroscopy.

Referring to FIG. 23F, the 213x layer is etched in a photolithographic process utilizing AZ5214 as the preferred photoresist and free methyl radicals as described as the etching reagent. This method provides a plurality of light sensitive segments 213x, 213Bx and 213Cx. These correspond to the photosensitive segments 224Bx, 224Dx, 224Fx, 224Hx and 2241x shown in Fig. 21. A perspective view of the structure obtained in the step shown in Fig. 23F is shown in Fig. 23G.

Referring now to FIG. 23H, a layer of mercury telluride and cadmium 240x having an alloy ratio x = 0.2 is formed by drawing using the MOCVD or MBE method cited above on the surface of the structure. This layer 240x covers the surface of the layer 212x as well as the detector segments 213Ax, 213Bx and 213Cx.

Referring to a top view of the 200x or 300x detectors, in Fig. 231, the 240x layer is patterned and etched by photolithographic techniques to remove material from the 240x layer between the rows. previously formed photosensitive segments, such as a row comprising the 213Ax, 213Bx and 213Cx segments. The photosensitive segments are sketched between the punctured lines.

Referring to Fig. 23J, the layer 240x is further etched where it directly covers previously formed photosensitive segments, such as 213Ax, 213Bx and 213Cx. The remainder of the intermediate material includes non-photosensitive conductive segments 240Ax and 2408X. Figure 23K is a top view of the structure shown in Figure 23J. Continuous bands have been formed which include altered segments that are photosensitive to other segments that are conductive but non-photosensitive to the wavelength of the infrared radiation of interest.

Referring to FIG. 23L, there is shown the steps of adding a passivation layer 242x to one surface of the structure. This layer is preferably in a material such as zinc sulfide. Finally, contacts are formed on the appropriate conductive portion of the detector, as shown, for example a contact 244x. Such contacts are preferably indium. Finally, the entire device is provided with terminals and is encapsulated in a known manner. If it is desired to have an individual detector, an infrared window is provided in the package. In a focal plane array, a plurality of devices are provided in an evacuated environment where they receive an infrared image.

Fig. 24 is a schematic representation of the operating circuit of the detector 20x and similarly detectors 90x, 200x and 300x. In this figure 24, the detector segments, the photosensitive segments <B> included in the infrared detectors, </ B> are represented as signal sources such as 28Ax to 28Ex which are connected between the conductive terminals 46x and 48x (Figure 13). A bias signal is applied via a DC source 314x which is connected in series with a load resistor 321x between the conductive terminals 46x and 48x. When the detectors, which include the segments 28Ax and 28Ex, receive the energy of the infra red radiation captured, this energy is transformed into an impedance variable which changes the amplitude of the continuous polarization signal. which produces a detection signal between output terminals 320x and 322x. This is the output signal for a single pixel element in a <B> network of such circuits. </ B>

An array of detectors 324x is shown <B> in FIG. 25. This array 324x comprises a plurality of individual pixel detectors as represented by the detectors 326x. These 326x detectors may be any of the 20x, 90x, 200x or 300x detectors shown in Figures 13, 18, 19, 21 and 22. All <b> detectors in the 324x network can </ B > have a common polarization line but each must have a separate line for the output signal, 328x lines for 326x detectors. Each of the pixel detectors in the 324x <B> network has separate signal lines. </ B>

<B> The 324x network is a part of a 325x </ B> imaging system in infrared. All of the Pixel Detectors in the 324x array can produce an image as a result of <B> focusing infrared radiation on the 324x network surface using a 330x lens . The image is in the signal on the output signal lines such as 328x. In addition, all individual pixel detectors, such as 326x, may be fabricated on a single common substrate such as substrate 22x shown in FIG. 13.

Referring now to FIG. 26, there can be seen an infrared detector 400x which includes a plurality of photosensitive strips 402x, 404x, 406x, 408x, 410x and 412x which are disposed on a substrate layer 418x. The 402x to 412x bands comprise mercury cadmium telluride (TCM) which has a ratio x approximately equal to 0.15, which corresponds to an operating temperature of 300 K. The layer 418x is preferably cadmium.

The 402x to 412x strips have a thickness of about 0.5 microns, a width of 1 micron and a length of 50 microns. The layer 418x preferably has a thickness of 0.3 micron.

At opposite ends of the 402x to 412x strips are conductive elements 420x and 422x which are preferably mercury and cadmium telluride having an alloy ratio equal to or greater than 0.2. With this ratio, the elements 420x and 422x are electrically conductive but non-photosensitive in the 8 to 12 micron band at 300 K. Indium contacts 424x and 426x are respectively arranged above the conductive elements 420x and 422x and are electrically connected. to the 420x and 422x elements.

The layer 418x is disposed on a layer 430x which comprises zinc sulfide and has a thickness of about 0.1 microns.

A 432x aluminum layer is deposited between the 430x layer and a 434x epoxy bonding layer. The 432x layer is an infrared reflective plane and has a thickness of about 500 to 1000 angstroms. A 436x substrate, preferably sapphire, has a thickness of about 2 mm. The 434x epoxy layer connects the 432x aluminum layer to the 436x substrate.

Figs. 27A to 27H show a method for manufacturing the 400x detector shown in Fig. 26. It has much analogy to the manufacturing method described in Figs. 15A-15K. In FIG. 27A, a layer 442x of mercury and cadmium telluride having a coefficient x = 0.15 is drawn on the surface of a 440x dielectric sheet of cadmium and zinc telluride. The layer 442x will be etched, as described below, to become the 402x to 412x bands. A layer 418x of cadmium telluride is formed by drawing on the surface of the layer 442x.

In Fig. 27B, the layer 418x is thinned in the same manner as described above for the layer 76x with reference to Fig. 15B.

Referring to Fig. 27C, the layer 430x is drawn by drawing on the surface of the layer 418x. The aluminum layer 432x is formed on the surface of the layer 430x as described above for the plate 24x shown in FIG. 15E.

In Fig. 27D, a 134x epoxy layer is applied to the free face of the aluminum layer 432x to connect the 436x substrate to the rest of the structure.

Referring to Fig. 27E, the plate 440x has been removed in the same manner as the substrate 70x shown in Fig. 15F. The structure has been inverted in Figure 27E with respect to that shown in Figure 27D.

The layer 442x is thinned as shown in Fig. 27F, by a dry etching method using methyl radicals to obtain the desired thickness for the 402x to 412x strips. <B> In Figure 27G, a varnish </ B> to <B> hide 450x, </ B> as described above, is applied on layer 442x <B> and is <B> configured <B> to selectively attack the 442x layer to make the 402x to 412x bands. We then eliminate the 450x masking varnish. </ B>

<B> In Figure 27H, a 450x passivation layer is applied to the free face of the detector structure to protect it. This detector is supplemented by usual process steps of indium contact formation, terminal fixing and encapsulation.

The detector 400x, which is shown in FIG. 26, if compared to the detector 200x shown in FIG. 21, may have a lower detection capability than the 200x detector for the same dimen - </ b> sions and the same form; but it can be achieved much more easily because of its lower complexity and the reduced number of manufacturing steps. By </ B> <B> elsewhere the possibilities of operation are <B> little </ B> <B> near the same ones. </ B>

<B> Infrared detectors manufactured as <B> <B> described above have a greatly improved detection capability <B> <B> compared to previous models. </ B> This enhanced detection capability can to be <B> used as an alternative to reduce the need for <B> equipment <B> while maintaining a standard </ B> or sensitivity, using refrigeration equipment, a detector made in accordance with the present invention can have a greatly increased sensitivity.

The photosensitive segments described above <B> for the described embodiments are made of </ B> mercury and cadmium telluride having a specified alloy ratio <B>. This material is photoconductive, </ b> that is, a band gap material that <B> produces charge carriers in response to <B> a rayon - </ B > <B> incidentally. </ B> Photosensitive <B> elements can also be realized in a photovoltaic structure such as a pn junction of mercury and cadmium telluride that produces a voltage in response to incident <B> radiation. </ B> B>

To summarize, the present invention includes a method for making infared <B> detectors. These detectors have a plurality of elongated electrically conductive members and include photosensitive segments separated by, but not in contact with, non-photosensitive conductive segments. According to another aspect of the invention, electrically insulated parallel conducting lines are disposed immediately from the surface of the detector and spaced apart from each other by a distance of <B>. less than <B> the bandwidth of the radiation </ B> <B> to increase the infrared radiation pickup. </ B>

Although many embodiments of the <B> invention have been <B> shown in the accompanying drawings </ B> and described in the detailed description above, it is evident that The invention is not limited to the described embodiments, but is capable of many modifications, variations or substitutions without departing from the scope of the present invention.

Claims (3)

A detector for infrared radiation and shorter wavelengths characterized by comprising: an array of photodetector elements (10; 50; 132; 214; 260; 296; 20x; 300x, 326x, 400x) in a plane and spaced from each other by a distance less than about the wavelength of said radiation; a plurality of radiation collection structures (40; 72-86; 216-230; 262-276; 298,300; 324-328; 332; 402x-412x) connected respectively to said photodetector elements; a reflective plane (116.24x, 236x) for said radiation offset from the plane of said photodetector elements by a distance less than the wavelength of said radiation, in which the combination of said radiation collecting structures and said reflecting plane captures and transmits said radiation to said detector elements for generating a detection signal. 2. Detector according to claim 1, characterized in that each of the linear dimensions of said detector elements is less than the wavelength of said radiation. 3. A detector according to claim 1, characterized in that it comprises conductive lines connected to said radiation collecting structures for transmitting said detection signal. <4> </ B> A sensor according to claim 1, characterized in that said photodetector elements (10; 50; 132; 214; 260; 296; 20x; 300x; 326x; 400x) comprise mercury telluride and of cadmium. A detector according to claim 1, characterized in that said detector elements (10; 50; 132; 214; 260; 296; 20x; 300x; 326x; 400x) comprise indium antimonide. 6. Detector according to claim 1, characterized in that said photodetector elements comprise a semiconductor superstructure. 7. Detector according to claim 1, characterized in that said reflective plane for the radiation is a metal layer. 8. Detector according to claim 1, characterized in that said radiation reflecting plane is a multilayer dielectric. 9. Detector according to claim 1, characterized in that each of said radiation collecting structures comprises a dipole antenna. 10. A detector according to claim 1, characterized in that it comprises blocking contacts (120 126) for connecting said photodetector elements to said radiation collecting structures. 11. Radiation detector, characterized in that it comprises a periodic configuration of parallel, elongated, photoconductor or photovoltaic bandgap detectors (40; 72-86; 216-230; 262-276; 298,300; 324-328; 332; 402x-412x), said elements being spaced from each other by a distance which is less than about the wavelength of said radiation, said array of detector elements having a given radiation impedance ; means constituting a substructure (240; 280; 302; 322) for supporting said detecting elements and for providing an impedance adptation between the radiation impedance of said detector elements and the free-space radiation impedance ; and - means (46x, 48x, 115x, 117x, 227x, 229x) for electrically connecting said detector elements to produce a detection signal when said detector is exposed to said radiation. </ B> A detector according to claim 11, characterized in that each of the linear dimensions of said detector elements (10; 50; 132; 214; 260; 296; 20x; 300x; 326x; 400x) is smaller than at the wavelength of said <B> radiation. </ B> <B> 13. Detector according to claim 11, characterized in that said sub structure means (240; 280; 302; 322) comprise a dielectric plate (242; 222; 308; 330). carrying said detector elements on one of its faces and a metal layer on one opposite side. A detector according to claim 1, characterized by comprising upper structure means (286; 304) adjacent to said detector and opposite configuration of said elements. said upper structure means for providing an impedance match between said detector elements and said impedance in the open air. </ B> Detector according to claim 1, characterized in that said detector elements (10; 50; 132; 214; 260; 296; 20x; 300x; 326x; 400x) comprise mercury telluride and cadmium. A detector according to claim 1, characterized in that said sub structure means (240; 280; 302; 322) comprises first and second layers having different refractive indices. 17. A detector according to claim 16, characterized in that said first layer is of indium antimonide and said second layer is cadmium telluride. 18. A detector according to claim 1 to 11, characterized in that it comprises a second periodic configuration of parallel, elongate, photoconductive or photovoltaic bandgap detecting elements spaced from each other by a distance of is equal to or less than the wavelength of said radiation, said second detector element configuration being orthogonal to said first detector element configuration and disposed in a plane offset from said first detector and parallel detector configuration; thereto and means for electrically connecting said second detector element configuration to produce a detection signal when said detector is exposed to said radiation. 19. A method of manufacturing a device for the detection of radiation in the infrared range and the range of shorter wavelengths, characterized in that it comprises the following steps - forming a plurality of groups of segments photosensitive in a planar array, said photosensitive segments being responsive to said radiation and said photosensitive segments having a thickness less than the wavelength of said radiation, said photosensitive elements comprising a plurality of groups, each group comprising a plurality of ten light-sensitive segments arranged in an elongated configuration, the photosensitive segments of each group being offset from one another by a distance which is less than approximately said wavelength and the lateral dimensions of each of the photosensitive segments being less than said wavelength; forming a plurality of electrically conductive segments for interconnecting adjacent segments of said photosensitive segments in each of said groups, said electrically conductive segments not being photosensitive to said radiation, each group of said photosensitive segments as well as the conductive segments corresponding electrically conductive along their length; - forming a plane which is reflective for said radiation; said planar network of photosensitive segments and said reflective plane being offset from each other by a distance less than said wavelength; and - electrically connecting a plurality of said photosensitive segment groups in parallel to provide a conduction path for the detection signals produced by said photosensitive segments in response to said infrared radiation. 20. A method for manufacturing a device for the detection of infrared radiation according to claim 19, characterized in that said electrically conductive segments are placed in a parallel plane but offset with respect to the plane of said sensitive photo segments. 21. A method for manufacturing a device for detecting infrared radiation according to claim 19, characterized in that said electrically conductive segments are placed in a plane which is coplanar with the plane of said photosensitive segments. 22. A method for manufacturing a device for the detection of infrared radiation according to claim 19, characterized in that it comprises the step of forming a heterojunction at each interface between said photosensitive segments and said electrically conductive segments. 23. A method for manufacturing a device for the detection of infrared radiation according to claim 19, characterized in that it comprises the step of manufacturing insulating material for separating said reflective plane from said photosensitive segments, said insulating material being in contact with said photosensitive segments. said photosensitive segments. 24. A method for manufacturing a device for detecting infrared radiation according to claim 19, characterized in that the step of forming a reflective plane comprises forming an aluminum layer. 25. A method for manufacturing a device for the detection of infrared radiation according to claim 23, characterized in that it further comprises the step of forming a blocking junction at each interface between said photosensitive segments and said insulating material. .