Uncooled metallic bolometer

FIELD: physics.

SUBSTANCE: said utility invention relates to thermal photoreceivers for the detection of monochromatic radiation in the far infrared (IR) range and determining the angle of arrival of that radiation. The development may be used in spectrometric and astronomical instruments, special purpose equipment, and communication equipment. The metallic bolometer contains a non-transparent metallic film on an optical heat-insulating substrate placed in a vacuum container with a transparent window. A dielectric layer of a certain thickness is applied on the film surface. The film surface facing the window has a corrugated section illuminated with the radiation being detected; the section length is equal to the propagation length of the surface electromagnetic wave excited in the film. The corrugation period is calculated using a certain formula.

EFFECT: invention provides increase of device selectivity and increase of long-wavelength limit of operating range.

1 dwg

 

The invention relates to thermal sensors for the detection of monochromatic radiation in the far infrared (IR) range, called recently, terahertz (THz) (frequency from 0.1 to 10 THz), and determine the angle of arrival of this radiation. Development may find application in spectroscopy and astronomical instruments, machinery, means of communication by THz radiation.

It is known that for the detection of THz radiation is used mainly heat sinks (radiation thermocouples and bolometers) and photon receivers (vacuum solar cells and semiconductor photoshoprecovery) [1]. At sufficiently high power radiation is used pyroelectric receivers [2] or optical-acoustic elements of the cell [3]. All these types of receivers are non-selective or weakly selective in frequency, angle of arrival and polarization of the radiation. In addition, the long wavelength edge of the stage known uncooled bolometers is limited to 50 µm [4].

Creation of laser sources (solid-state, free electron, water vapor and methanol) THz radiation, synchrotron research and cosmic radiation, the development of THz communications and information processing, the use of THz radiation in medical tomography [5] have necessitated the development that accounts for the uncooled metal bolometers with the long border of their workspace, up to several tenths of a millimeter, and highly selective bandwidths, the angle of incidence and polarization of the detected radiation.

It is known that "...if necessary, the bolometer can make the election (by frequency) using an external filter or by introduction of appropriate selective dye in the organic film applied to the main absorbent layer gold mobile" [4]. However, this technique provides a very low selectivity of the bolometer.

Known selective photodetectors operating on the basis of the Schottky barrier. In these photodetectors detective monochromatic radiation excites the p-polarized surface electromagnetic wave (sew), which is accompanied by an increase in the strength of the radiation field in the semiconductor and increase the quantum efficiency of the receiver [6, 7]. In this case the excitation sew occurs only at a specific angle of incidence that is structurally provided by the creation of the corrugations on the border section "metal-semiconductor". The main disadvantage of these sensors is their limited workspace visible and near IR ranges.

The closest to the technical nature of the claimed device is uncooled metal bolometer consisting of an opaque metal square the NCI, printed on a heat insulating optical substrate placed in the vacuum container provided with a transparent window [4]. The free surface of the film covered with a layer of gold or platinum mobile, ensuring the absorption of radiation. The main disadvantages of the known device are neselektivno (frequency, angle of arrival and polarization of the radiation and longwave boundary (50 µm) operating range.

The technical result of the invention is to improve the selectivity of the device (in terms of frequency, angle of arrival and polarization of the radiation) and the increase in longwave boundary working range up to 100 μm (0.1 mm).

The technical result is achieved in that in an uncooled metal bolometer containing an opaque metal film on the optical insulating substrate placed in the evacuated container having a transparent window on the surface of the film deposited dielectric layer of thickness dodefined by the formula:

where nl- refractive index material layer, and λ is the wavelength in vacuum, while facing the window film surface is illuminated detektivami radiation corrugated area length equal to the length distribution induced in the film surface e is ectromagnetic waves (sew), moreover, the period Λ corrugation is calculated by the formula:

where ϕ - the angle of incidence of the radiation, nSewis the refractive index sew.

The heat sensitive element bolometer detektivami radiation is provided in the heat loss sew as its distribution along the film. This effect is known based bolometric method of registration excitation sew [8, 9].

The selectivity of the bolometer on the polarization of the detected radiation follows from the fact that the sensitive surface of the metal element of the bolometer can be an electromagnetic wave only p-polarization in which the electric field vector has a nonzero component perpendicular to the surface [10].

The selectivity of the item in terms of frequency and angle of arrival of the detected radiation due to the resonant nature photon excitation sew. The conversion of the incident (informative) radiation in sew occurs when the equality of the tangential components of the wave vector sew kxthe sum of the tangential component of the wave vector of the radiation koand corrugation kΛ. This condition can be written in the following form [11]:

where Λ - period of the corrugation, ko=2π/λ.

The offset of the long-wave boundary of the working range up to 0.1 mm is achieved due to the increase in thermal energy absorption fields sew in the metal film when applied to the surface of the dielectric layer thickness d [12]. Applying a layer leads to a redistribution of the field sew from the environment in the film, and the diffusion length sew in the THz range is reduced by five orders of magnitude and is only several tenths of a millimeter. Accordingly, and heat loss sew.

The drawing shows a diagram of the inventive device, where the numbers denote: 1 - transparent window; 2 - vakuumirovaniya container; 3 - opaque metal film; 4 - heat-insulating optical substrate; 5 - dielectric layer of thickness doa 6 - environment (vacuum), 7 - electrical contacts.

The claimed bolometer operates as follows. Detective radiation with non-zero R-component penetrates through the window 1 in the container 2, falls on the corrugated stretch film 3 deposited on the substrate 4, angle ϕsatisfying the equality (1), and excites sew on the boundary film 3 - layer 5". Field sew transferred in three environments: the film 3, layer 5 and 6 vacuum. In the heat loss sew in the metal film is heated. The temperature of the film increases its electrical resistance, which registers connected to the contacts 7 of the measuring device, such as a bridge circuit.

In order to reduce the radiation losses of the surface of the film 3 outside the window is made flat. So about what atom, all the radiation energy is converted to sew on shirred stretch film is transformed into heat energy liberated in the film.

As an example of application of the inventive device, consider registering it using p-polarized radiation with a wavelength of λ=10 μm, modulated with a frequency of 1000 Hz. As a material of the metal film will choose platinum, having the following physical characteristics: density γ=21500 kg/m3temperature coefficient β=4·10-3deg-1, specific heat C=136 j/(kg·hail), resistivity ρ=10-7Ohm/m, the complex dielectric permittivity ε=-5400+j·33000 (where j is an imaginary unit). The length of the platinum element is put equal to 10 mm, width of 1 mm, thickness of 0.1 μm. The substrate element will select nitroglycern [4], on the surface of which is formed bumps with the following parameters: period Λ=77 μm, the amplitude (distance from the optical surface of the substrate up to the crest of the flute) δ=50 μm, the length (distance along the plane of incidence of the radiation) 1.0 mm and the width (distance perpendicular to the plane of incidence) is not less than the width of the element, i.e. not less than 1 mm, the power density of the detected radiation is put equal to 10-2W/mm2while the efficiency of conversion of radiation in the sew - 50% [15]. D. the I maximum energy absorption fields sew on the surface of the platinum element is coated with the layer thickness Germany d o=7.0 µm with a refractive index of nl=4,0.

In this case, the radiation is converted to sew with maximum efficiency (50%) at an angle of incidence ϕ=30°14'. The length distribution sew L (the distance at which the energy of the field sew decreases in e=2,718 times) is only 1 mm, which corresponds to the attenuation factor PSUs α=1/L, equal to 103m-1.

Then, according to [9], the change in the electrical resistance ΔR platinum element when the fall of a single radiation pulse duration Δt=10-3c will be an amount equal to 0.04 Ohms. Such value ΔR can be confidently registered by the measuring bridge of the Wheatstone on the overall resistance of the sensing element (at room temperature), equal to about 10 Ohms.

Thus, the claimed device: 1) allows you to register at room temperature THz radiation with long wavelength boundary to 110 μm; 2) ensures the selectivity of the receiving polarization, angle of incidence and the wavelength of the radiation.

Sources of information

1. Smith, R., Jones, F., Casmer R. Detection and measurement of infrared radiation. // M: Foreign literature, 1959. - Ch.3-4. - p.63-171.

2. Lines M, the Voice of A. ferroelectrics and related materials. // M.: Mir, 1981. - S-623.

3. Pankratov N.A. Selective optic the acoustic receiver with an optical microphone. // Optical-mechanical industry. - 1960. No. 1. - p.37-48.

4. Scholl J., Marfan I., Munch M, Torelli P., Combat P. detectors of infrared radiation. // M.: Mir, 1969. - s-186. (prototype)

5. P.H. Siegel Terahertz technology // IEEE Transactions on Microwave Theory and Techniques. - 2002. - v.50. - No.3. - p.910-955.

6. Glass A.M., A.M. Johnson, P.F. Liao-H. Photodetector // Patent GB 2131229 And (MKI4H01L 31/02). - 1984.

7. Belyakov L.V., Seseli O.M. Surface electromagnetic waves and photodetectors. // Physics and technics of semiconductors. - 1991. - V.25. - VIP. - s-1296.

8. Yuan-Lin X., Hua Li, Yue-Liang Z. et al. Bolometric observation of nonradia-tive decay of surface plasmons in silver. // Applied Physics (A). - 1989. - v.48. - No.5. - p.497-500.

9. Bolshakov M.M., A.K. Nikitin, A.A. Tishchenko, Samodurov SCI Device for determining the absorption coefficient sew metal films. // Author, the Holy of the USSR №1684634 from 15.06.1991,

10. Zhizhin G.N., Moskaleva M.A., SAMINA E.V., Yakovlev V.A. Distribution sew on metal surfaces. // Ch.3. (p.70-104) in the book "Surface polaritons. Electromagnetic waves at surfaces and interfaces environments" Ed. by Wymagania and Dells. - M.: Nauka, 1985. - 525 S.

11. Nikitin, A., A.A. Tishchenko Surface electromagnetic waves and their application. // Foreign Radioelectronics. - 1983. No. 3. - ñ.38-56.

12. Zhizhin G.N., Nikitin, A., Bogomolov GD, V.V. Zavyalov, Jeong Jung MC, Lee Bang Cheol, Seong Hee Pak, Hyuk Jin Cha. Absorption of surface plasmon largercapacity in the structure of the metal-coating layer-to-air. // Optics and spectroscopy, 2006, T, No. 5, s-802.

13. Seymour R.J., Krupczak J.J., G.I. Stegeman High efficiency coupling to the overcoated surface plasmon mode in the far infrared. // Applied Physics Letters, 1984, v.44, No.4, p.373-375.

Uncooled metal bolometer containing an opaque metal film on the optical insulating substrate placed in the evacuated container having a transparent window, wherein the surface of the film deposited dielectric layer of thickness dodetermined by the formula

where nl- refractive index material layer, and λ is the wavelength in vacuum, while facing the window film surface is illuminated detektivami radiation corrugated area length equal to the length distribution induced in the film surface electromagnetic waves (sew), and the term Λ corrugation is calculated by the formula

where ϕ - the angle of incidence of the radiation, nSewis the refractive index sew.



 

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