Search

US-12628560-B2 - Absorber, a detector comprising the absorber, and a method of fabricating the absorber

US12628560B2US 12628560 B2US12628560 B2US 12628560B2US-12628560-B2

Abstract

An absorber for absorbing electromagnetic radiation including a first layer with hydrogenated carbon, and a second layer with carbon, and the first layer is less absorbing than the second layer.

Inventors

  • Desmond Gibson
  • David Hutson
  • SHIGENG SONG

Assignees

  • UNIVERSITY OF THE WEST OF SCOTLAND

Dates

Publication Date
20260512
Application Date
20230413
Priority Date
20201013

Claims (15)

  1. 1 . An absorber for absorbing electromagnetic radiation comprising: a first layer comprising hydrogenated carbon; a second layer comprising carbon; and one or more intermediate layers; wherein: the one or more intermediate layers are sandwiched between the first layer and the second layer; the first layer is less absorbing than the second layer; the first layer is an anti-reflection layer; the second layer is an absorbing layer; the first layer has a hydrogen content that is greater than the hydrogen content of the second layer; the first layer has a hydrogen content that is greater than the hydrogen content of the one or more intermediate layers; and the one or more intermediate layers has a hydrogen content that decreases successively from the first layer to the second layer.
  2. 2 . The absorber of claim 1 , wherein the second layer comprises non-hydrogenated carbon.
  3. 3 . The absorber of claim 1 , wherein the absorber is for absorbing electromagnetic radiation at infrared wavelengths.
  4. 4 . The absorber of claim 3 , wherein the absorber is for absorbing electromagnetic radiation within a wavelength range of 2 μm to 18 μm.
  5. 5 . The absorber of claim 3 , wherein the absorber is for absorbing electromagnetic radiation within a wavelength range of 5 μm to 12 μm.
  6. 6 . The absorber of claim 1 , wherein the absorber is configured to be a broadband absorber.
  7. 7 . The absorber of claim 1 , wherein the first layer, the second layer and the one or more intermediate layers form a free standing structure.
  8. 8 . The absorber of claim 1 , further comprising a substrate or a membrane.
  9. 9 . A detector for detecting electromagnetic radiation comprising: an absorber for absorbing electromagnetic radiation comprising: a first layer comprising hydrogenated carbon; a second layer comprising carbon; and one or more intermediate layers; wherein: the one or more intermediate layers are sandwiched between the first layer and the second layer; the first layer is less absorbing than the second layer; the first layer is an anti-reflection layer; the second layer is an absorbing layer; the first layer has a hydrogen content that is greater than the hydrogen content of the second layer; the first layer has a hydrogen content that is greater than the hydrogen content of the one or more intermediate layers; and the one or more intermediate layers has a hydrogen content that decreases successively from the first layer to the second layer.
  10. 10 . The detector of claim 9 , further comprising a CMOS chip, wherein the CMOS chip comprises the absorber.
  11. 11 . The detector of claim 9 , further comprising a heat sensitive element configured to detect heating of the absorber when it absorbs electromagnetic radiation.
  12. 12 . A method of fabricating an absorber for absorbing electromagnetic radiation, the absorber comprising: a first layer comprising hydrogenated carbon; a second layer comprising carbon; and one or more intermediate layers; wherein: the one or more intermediate layers are sandwiched between the first layer and the second layer; the first layer is less absorbing than the second layer; the first layer is an anti-reflection layer; the second layer is an absorbing layer; the first layer has a hydrogen content that is greater than the hydrogen content of the second layer; the first layer has a hydrogen content that is greater than the hydrogen content of the one or more intermediate layers; and the one or more intermediate layers has a hydrogen content that decreases successively from the first layer to the second layer, the method comprising: depositing carbon to form at least one of the first layer and the second layer.
  13. 13 . The method of claim 12 , wherein depositing carbon comprises sputtering the carbon.
  14. 14 . The method of claim 13 , comprising: controlling the hydrogenation of the carbon during sputtering to control the absorption characteristics of the first layer and/or the second layer.
  15. 15 . The method of claim 14 , wherein the absorber is fabricated in a single pulsed DC sputtering process, and wherein the first and second layers are fabricated by the controlling of the hydrogenation of the carbon during sputtering.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a national stage entry of International Application No. PCT/GB2021/052388 filed on Sep. 15, 2021, which claims priority from United Kingdom Application No. 2016210.3 filed on Oct. 13, 2020, the contents of each of which are incorporated by reference herein in its entirety. BACKGROUND 1. Field of the Disclosure The present disclosure relates to an absorber for absorbing electromagnetic radiation, and a method of fabricating the absorber. In particular, the present disclosure relates to an absorber for use in an electromagnetic radiation detector, that may, for example, be used to detect electromagnetic radiation at infrared wavelengths. 2. Description of the Related Art FIG. 1 is a schematic of a thermopile 100 that is configured to function as a thermopile infrared (IR) detector. The thermopile 100 may be referred to as a thermopile chip. The thermopile 100 comprises a substrate 102, supporting layers and/or passivation layers 104 and an absorber 110. In FIG. 1(a), three layers form the supporting and/or passivation layers 104. Thermopile infrared (IR) detectors may be used as sensing elements for non-contact infrared thermometers. Supporting layers are used to support the absorber 110 and passivation layers may be used as part of the lift off process that is used to define the overall structure. In operation, IR radiation that is incident on the thermopile 100 is absorbed by the absorber 110, resulting in the absorber increasing in temperature. This results in temperature difference arising between a hot junction 112 and a cold junction 114. Based on the Seebeck effect, the thermopile 100, which comprises a plurality of thermocouples (not shown), transforms the temperature difference between the hot and cold junctions 112, 114 into an output voltage. It will be appreciated that the hot junction 112 refers to the general area including the absorber 110 and immediately surrounding the absorber 110, whereas the cold junction 114 refers to an area outside the hot junction 112 region. In effect the hot junction 112 and cold junction 114 are general areas showing temperature difference, with the hot junction 112 being the warmer of the two areas when radiation is absorbed, thereby resulting in the required temperature difference for operation of the thermopile 100. Silicon, a primary substrate material, is used in many microelectromechanical systems (MEMS) based thermopile devices, such as the thermopile 100, due to its low cost and complementary metal oxide semiconductor (CMOS) processing compatibility. The substrate 102 of the thermopile 100 is silicon and may be provided as a semiconductor wafer. A porous metal (named “metal black”, such as gold-black, silver-black, and platinum-black) is typically used as the absorber 100. Metal black can exhibit high absorption properties (>90%) and a wide absorption band. Metal black absorbers are presented in “Absorbing layers for thermal infrared detectors; W. Lang, K. Kuhl, H. Sandnaier; Sens. Actuators, A 34 (1992) 234-248” and “120×90 element thermoelectric infrared focal plane array with precisely patterned Au-black absorber; M. Hirota, Y. Nakajima, M. Saito, M. Uchiyama; Sense. Actuators, A 135 (2007) 146-161. However, porous metals such as metal black are easily destroyed by contact, they difficult to pattern and they are incompatible with CMOS processing because their dendritic and soft structures make them too fragile for standard techniques like lithography and etching. Furthermore, their preparation process is much complex and costly. A silicon nitride (Si3N4) layer, a silicon dioxide layer (SiO2) layer or a sandwich film structure comprising a silicon nitride layer sandwiched between two silicon dioxide layers (SiO2/Si3N4/SiO2) is also often used as the absorber 110 of the thermopile 100. Such a structure may be referred to as a “membrane”. However, such a membrane provides low IR absorption and a narrow spectral absorption range thereby inhibiting its usefulness for IR detection. Additionally, these membranes are difficult to pattern and are not compatible with CMOS; the dendritic and soft structures make them too fragile for standard CMOS techniques like lithography and etching. Furthermore, their preparation process is complicated and costly. Examples of such membranes are presented in “Thermoelectric infrared sensors by CMOS technology; R. Lenggenhager, H. Baltes, J. Peer, M. Forster; IEEE Electron Device Lett. 13 (1992) 454-456”, “Far-infrared sensor with LPCVD-deposited low stress Si-rich nitride absorber membrane; F. Jutzi, D. H. B. Wicaksono, G. Pandraud, N. de Rooij, P. J. French; Part 2. Thermal property, and sensitivity, Sens. Actuators, A 152 (2009)” and “Design, fabrication and characterization of a front etched micromachined thermopile for IR detection, D. H. Xu, B. Xiong, Y. L. Wang, J. Micromech. Microeng. 20 (2010) 115004”. SUMMARY It is desirable to provide an absorber suitable for d