INFRARED BOLOMETER AND METHOD FOR THE MANUFACTURE THEREOF

Abstract: An inventive infrared bolometer having a decreased NETD and an increased responsivity and detectivity, which comprises an active matrix level (110) including a substrate (112) and a pair of connecting terminals (114); a support level (120) provided with a pair of bridges (122) and a pair of conduction lines (124); an absorption level (130) including a bolometer element (132) surrounded by an absorber (131), wherein the bolometer element (132) has a vertical undulating shape and a horizontal serpentine shape; and a pair of posts (140), each of the posts (140) including an electrical conduit (142), each ends of the bolometer element (132) being electrically connected to the respective connecting terminal (114) through the respective conduit (142) and the respective conduction line (124). The bolometer element (132) has the horizontal serpentine shape and the vertical undulation shape to maximize the total length of the bolometer element in a given space or area, thereby decreasing the NETD and increasing the responsivity and detectivity in the infrared bolometer.

Description: INFRARED BOLOMETER AND METHOD FOR THE MANUFACTURE THEREOF TECHNICAL FIELD OF THE INVENTION The present invention relates to infrared bolometer; and, more particularly, to infrared bolometer having a decreased NETD and an increased responsivity and detectivity. BACKGROUND ART A radiation detector is a device that produces an output signal which is a function of the amount of radiation that is incident upon an active region of the detector. Infra-red detectors are those detectors which are sensitive to radiation in the infra-red region of the electromagnetic spectrum. There are two types of infra-red detectors, thermal detectors including bolometers and photon detectors. The photon detectors function based upon the number of photons that are incident upon and interact with electrons in a transducer region of the detector. The photon detectors, since they function based on direct interactions between electrons and photons, are highly sensitive and have a high response speed compared to the bolometers. However, they have a shortcoming in that the photon detectors operate well only at low temperatures, necessitating a need to an incorporate therein an additional cooling system. The bolometers function, on the other hand, based upon a change in the temperature of the transducer region of the detector due to absorption of the radiation. The bolometers provide an output signal, i.e., a change in the resistance of materials (called bolometer elements) , that is proportional to the temperature of the transducer region. The bolometer elements have been made from both metals and semiconductors. In metals, the resistance change is essentially due to variations in the carrier mobility, which typically decreases with temperature. Greater sensitivity can be obtained in high-resistivity semiconductor bolometer elements in which the free- carrier density is an exponential function of temperature. In Figs. 1 and 2, there are shown a perspective view and a cross sectional view illustrating a three- level bolometer 100, disclosed in U.S. Ser. Application No. 09/102,364 entitled "BOLOMETER HAVING AN INCREASED FILL FACTOR" . The bolometer 100 comprises an active matrix level 10, a support level 20, a pair of posts 40 and an absorption level 30. The active matrix level 10 has a substrate 12 including an integrated circuit (not shown) , a pair of connecting terminals 14 and a protective layer 16. Each of the connecting terminals 14 made of a metal is located on top of the substrate 12. The protective layer 16 made of, e.g., silicon nitride (SiN ) , covers the substrate 12. The pair of connecting terminals 14 are electrically connected to the integrated circuit. The support level 20 includes a pair of bridges 22 made of silicon nitride (SiN χ ) , each of the bridges 22 having a conduction line 24 formed on top thereof. Each of the bridges 22 is provided with an anchor portion 22a, a leg portion 22b and an elevated portion 22c, the anchor portion 22a including a via hole 26 through which one end of the conduction line 24 is electrically connected to the connecting terminal 14, the leg portion 22b supporting the elevated portion The absorption level 30 is provided with a bolometer element 32 surrounded by an absorber 31 and an IR absorber coating 33 formed on top of the absorber 31. The absorber 31 is fabricated by depositing silicon nitride before and after the formation of the bolometer element 32 to surround the bolometer element 32. Titanium (Ti) is chosen as the material for bolometer element 32 because of the ease with which it can be formed. Serpentine shape gives the bolometer element 32 to high resistivity. Each of the posts 40 is placed between the absorption level 30 and the support level 20. Each of the posts 40 includes an electrical conduit 42 made of a metal, e.g., titanium (Ti) , and surrounded by an insulating material 44 made of, e.g., silicon nitride (SiN χ ) . Top end of the electrical conduit 42 is electrically connected to one end of the serpentine bolometer element 32 and bottom end of the electrical conduit 42 is electrically connected to the conduction line 24 on the bridge 22, in such a way that each ends of the serpentine bolometer element 32 in the absorption level 30 is electrically connected to the integrated circuit of the active matrix level 10 through the electrical conduits 42, the conduction lines 24 and the connecting terminals 14. When exposed to infra-red radiation, the resistivity of the serpentine bolometer element 32 increases, causing a current and a voltage to vary, accordingly. The varied current or voltage is amplified by the integrated circuit, in such a way that the amplified current or voltage is read out by a detective circuit (not shown) . Three of the most important factors determining the performance of the infrared bolometer are the NETD (Noise Equivalent Temperature Difference), the responsivity and the detectivity, all of which are proportional, either inversely or directly, to the resistivity of the bolometer element. As the larger the resistivity is, the lower NETD is and the larger responsivity and the larger detectivity are. Accordingly, it is necessary for the bolometer element to increase the resistivity in a given space or area. DISCLOSURE OF THE INVENTION It is, therefore, a primary object of the present invention to provide an infrared bolometer having a decreased NETD and an increased responsivity and detectivity. It is another object of the present invention to provide a method for the manufacture of such infrared bolometer. In accordance with one aspect of the present invention, there is provided an infra-red bolometer having a decreased NETD and an increased responsivity and detectivity, which comprises: an active matrix level including a substrate and a pair of connecting terminals; a support level provided with a pair of bridges and a pair of conduction line; an absorption level including a bolometer element surrounded by an absorber, the bolometer element being vertically undulated; and a pair of posts, each of the posts including an electrical conduit, each ends of the bolometer element being electrically connected to the respective connecting terminal through the respective conduit and the respective conduction line. In accordance with another aspect of the present invention, there is provided a method for the manufacture an infra-red bolometer having a decreased NETD and an increased responsivity and detectivity, the method comprising a step of: preparing an active matrix level including a pair of connecting terminals; forming a first sacrificial layer including a pair of empty cavities; forming a supporting level including a pair of bridges and a pair of conduction lines; forming a second sacrificial layer including a pair of empty slots; forming a pair of posts in the pair of empty slots; depositing a lower absorber layer; partially etching the lower absorber layer; forming a bolometer element; forming an upper absorber layer; and removing the first and the second sacrificial layer, thereby forming the infrared bolometer. BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, wherein: Fig. 1 shows a perspective view setting forth an infrared bolometer previous disclosed; Fig. 2 presents a schematic cross sectional view depicting the infrared bolometer taken along A - A in Fig. 1; Fig. 3 shows a schematic cross sectional view setting forth an infrared bolometer in accordance with the present invention; Figs. 4A and 4B provide schematic cross sectional views depicting an absorption level of the infrared bolometer taken along its row and column directions, respectively; and Figs. 5A to 5G present schematic cross sectional views illustrating a method for the manufacture of the infrared bolometer in accordance with the present invention. MODES OF CARRYING OUT THE INVENTION There are provided in Figs . 3 , 4A to 4B and 5A to 5G a schematic cross sectional view setting forth an infrared bolometer 200, schematic cross sectional views depicting an absorption level 130 of the infrared bolometer 200 taken along its row and column directions, schematic cross sectional views illustrating a method for the manufacture of the infrared bolometer 200 in accordance with the present invention, respectively. It should be noted that like parts appearing in Figs. 3, 4A to 4B and 5A to 5G are represented by like reference numerals. The inventive bolometer 200 shown in Fig. 3 comprises an active matrix level 110, a support level 120, a pair of posts 140 and an absorption level 130. The active matrix level 110 has a substrate 112 including an integrated circuit (not shown) , a pair of connecting terminals 114 and a protective layer 116. Each of the connecting terminals 114 made of a metal is located on top of the substrate 112 and is electrically connected to the integrated circuit. The protective layer 116 made of, e.g., silicon nitride (SiN ) , covers the substrate 112 to prevent the connecting terminals 114 and the integrated circuit from damaging chemically and physically during the manufacturing of the infrared bolometer 200. The support level 120 includes a pair of bridges 122 made of an insulating material, e.g., silicon nitride (SiN χ ) , silicon oxide (Si0 2 ) or silicon oxy- nitride (SiOx v Ny) , and a pair of conduction lines 124 made of a metal, e.g., titanium (Ti) , wherein each of the conduction lines 124 is placed on top of the respective bridge 122. Each of the bridges 122 is provided with an anchor portion 122a, a leg portion 122b and an elevated portion 122c, the anchor portion 122a including a via hole 126 through which one end of each of the conduction lines 124 is electrically connected to the respective connecting terminal 114, the leg portion 122b supporting the elevated portion 122c. The absorption level 130 is provided with a bolometer element 132 surrounded by an absorber 131, an reflective layer 133 formed at bottom of the absorber 131 and an IR absorber coating 134 positioned on top of the absorber 131, as shown in Figs. 4A and 4B. The absorber 131 made of an insulating material having an low heat-conductivity, e.g., silicon nitride (SiN ) , silicon oxide (SiO χ ) or silicon oxy-nitride (SiO χ N ) is fabricated by depositing the insulating material before and after the formation of the bolometer element 132 to surround the bolometer element 132. The bolometer element 132 is made of metal, e.g., titanium, and has a serpentine shape horizontally and an undulation shape vertically to provide the infrared bolometer 200 with the decreased NETD and the increased responsivity and detectivity by increasing the total length of the bolometer element 132. The vertical undulation shape of the bolometer element 132 obtained by partial etching of the insulating material of the absorber 131 before the depositing the bolometer element 132 and the horizontal serpentine shape thereof is achieved by patterning the bolometer element 132 after it has been deposited. The reflective layer 133 is made of a metal, e.g., Al or Pt, and is used for returning the transmitted IR back to the absorber 131. The IR absorber coating 134 is made of, e.g., black gold, and is used for reinforcing an absorption efficiency for the incident IR. Returning in Fig. 3, each of the posts 140 is placed between the absorption level 130 and the support level 120. Each of the posts 140 includes an electrical conduit 142 made of a metal, e.g., titanium (Ti) , and surrounded by an insulating material 144 made of, e.g., silicon nitride (SiN χ ) , silicon oxide (SiO) or silicon oxy-nitride (SiO N ) . Top end of each of the electrical conduits 142 is electrically connected to one end of the bolometer element 132 and bottom end of the electrical conduit 142 is electrically connected to the conduction line 124 on the bridge 122, in such a way that each ends of the bolometer element 132 in the absorption level 130 is electrically connected to the integrated circuit of the active matrix level 110 through the respective electrical conduits 142, the respective conduction lines 124 and the respective connecting terminals 114. Figs. 5A to 5G provide schematic cross sectional views illustrating a method for the manufacturing an infrared bolometer 200 in accordance with the present invention. The process for manufacturing the infrared bolometer 200 begins with preparing the active matrix level 110 including a substrate 112 having an integrated circuit (not shown) , a pair of connecting terminals 114 and a protective layer 116, as shown in Fig. 5A. Each of the connecting terminals 114 is electrically connected to the integrated circuit . The protective layer 116 covers the substrate 112 and the connecting terminals 114. Subsequently, a first sacrificial layer 150 including a pair of empty cavities 155 is formed on top of the active matrix level 110 by depositing a poly-Si of the first sacrificial layer 150 and partially etching thereof, as shown in Fig. 5B . In a following step, there is formed on top of the first sacrificial layer 150 a supporting level 120 including a pair of bridges 122 made of an insulating material, e.g., silicon oxide, silicon nitride or silicon oxy-nitride, and a pair of conduction lines 124 made of a metal, e.g., Ti, as shown in Fig. 5C, wherein each of the conduction lines 124 is electrically connected to the respective connecting terminal 114 through a via hole 126. This step is achieved by depositing and patterning the insulating material of the bridge 122 and the metal of the conduction lines 124, respectively. Thereafter, a second sacrificial layer 160 including a pair of empty slots 165 is formed on top of the supporting level 120 by depositing and partially etching a poly-Si of the second sacrificial layer 160, as shown in Fig. 5D. In a next step, a pair of posts 140 are formed in the pair of empty slots 165, each of the posts 140 including an electrical conduit 142 surrounded by an insulating material 144, as shown in Fig. 5E . Bottom end of each of the electrical conduits 142 is connected to the respective conduction line 124. In an ensuing step, an absorption level 130 is formed on top of the second sacrificial layer 160 and the posts 140, the absorption level 130 including an absorber 131 made of an insulating material, e.g., silicon oxide, silicon nitride or silicon oxy-nitride, a bolometer element 132 made of titanium, a reflective layer 133 made of a metal, e.g., Al or Pt , and an IR absorber coating 134 made of, e.g., black gold, as shown in Fig. 5F. This step is achieved by following the procedures described herebelow. First, a metal of the reflective layer 133 is deposited by using a sputtering method. Next, a lower absorber layer (not shown) is deposited by using a CVD method and is partially etched by using a photolithography method. Thereafter, a bolometer element material (not shown) is deposited on top of the lower absorber layer, wherein the partial etching of the lower absorber layer provides the bolometer element material with a vertical undulation shape, and the bolometer element material is then patterned into have a horizontal serpentine shape, thereby forming the bolometer element 132. Subsequently, an upper absorber layer (not shown) is deposited to surround the bolometer element 132, thereby forming the absorber 131. Continuously, the IR absorber coating 134 is formed on top of the absorber 131, thereby forming the absorption level 130. Finally, the first and the second sacrificial layer 150, 160 are entirely removed by using an isotropic etching method with an etchant, e.g., XeF 2 , to thereby form the infrared bolometer 200, as shown in Fig. 5G. Alternatively, the partial etching step for providing the bolometer element 132 with the vertical undulation shape can be applied to the second sacrificial layer 160 or the reflective layer 133 instead of the lower absorber layer in accordance with the other embodiments of the present invention. When exposed to infrared radiation, the resistivity of the bolometer element 132 changes, causing a current and a voltage to vary, accordingly. The varied current or voltage is amplified by the integrated circuit, in such a way that the amplified current or voltage is read out by detective circuit (not shown) . In the infrared bolometer of the present invention, the bolometer element has the horizontal serpentine shape and the vertical undulation shape to maximize the total length of the bolometer element in a given space or area, thereby decreasing the NETD and increasing the responsivity and detectivity in the infrared bolometer. While the present invention has been described with respect to certain preferred embodiments only, other modifications and variations may be made without departing from the scope of the present invention as set forth in the following claims.

Claims: What is claimed is : 1. A infrared bolometer comprising: an active matrix level including a substrate and a pair of connecting terminals; a support level provided with a pair of bridges and a pair of conduction lines; an absorption level including a bolometer element surrounded by an absorber, the bolometer element being vertically undulated; and a pair of posts, each of the posts including an electrical conduit, wherein each ends of the bolometer element of the absorption level is electrically connected to the respective connecting terminal through the respective electrical conduit and the respective conduction line. 2. The bolometer of claim 1, wherein the bolometer element has a horizontal serpentine shape. 3. The bolometer of claim 1, wherein the active matrix level further includes a protective layer formed on top thereof. 4. The bolometer of claim 1, wherein the absorption level further includes a reflective layer formed at bottom of the absorber. 5. The bolometer of claim 4, wherein the absorption level further includes an IR absorber coating formed on top of the absorber. 6. A method for the manufacture an infrared bolometer comprising the steps of: preparing an active matrix level including a substrate and a pair of connecting terminals; forming a first sacrificial layer including a pair of empty cavities; forming a supporting level including a pair of bridges and a pair of conduction lines; forming a second sacrificial layer including a pair of empty slots; forming a pair of posts in the pair of empty slots ; depositing a lower absorber layer; partially etching the lower absorber layer; forming a bolometer element; depositing an upper absorber layer, thereby forming an absorption level; and removing the first and the second sacrificial layer to thereby form the infrared bolometer. 7. The method of claim 6, wherein the step of partial etching of the lower absorber layer provides the bolometer element with a vertical undulation shape. 8. The method of claim 6, wherein the step of forming the bolometer element is provided with depositing a metal of the bolometer element and patterning the metal of the bolometer element into a horizontal serpentine shape . 9. The method of claim 6, wherein the lower absorber layer is same material with the upper absorber layer. 10. The method of claim 6 further comprising a step of forming a protective layer on top of the active matrix level . 11. The method of claim 6 further comprising a step of forming a reflective layer before the step of depositing the lower absorber layer. 12. The method of claim 6 further comprising a step of forming an IR absorber coating after the step of depositing the upper absorber layer. 13. The method of claim 6 comprising a step of partial etching of the second sacrificial layer instead of the step of partial etching of the lower absorber layer. 14. The method of claim 10 comprising a step of partial etching of the reflective layer instead of the step of partial etching of the lower absorber layer.

Inventors: JU SANG BAEK, JU, SANG, BAEK
Applicants: DAEWOO ELECTRONICS CO LTD, DAEWOO ELECTRONICS CO., LTD.
Application year: 1998
Main classification: G01J5
IPC codes: G01J1, G01J5, H01L27, H04N5