A terahertz detector with a planar equiangular spiral antenna structure and a method for manufacturing the same

Abstract

The present invention proposes a terahertz detector with a planar equiangular spiral antenna structure and a preparation method thereof, wherein a silicon dioxide support layer is grown on a silicon substrate; a hexanitrogen pentaniobium thin film thermal-sensitive layer is grown on the silicon dioxide support layer, and the silicon dioxide support layer and the silicon substrate are photolithographically and etched by designing a circular etching window to form a hexanitrogen pentaniobium microbridge suspended structure; the planar equiangular spiral antenna also serves as a coupling antenna and an electrode layer, and is located on the hexanitrogen pentaniobium thin film thermal-sensitive layer, and the central feed structure of the planar equiangular spiral antenna is directly connected to the two ends of the hexanitrogen pentaniobium microbridge. The present invention solves the problems of low detection bandwidth of conventional hexanitrogen pentaniobium terahertz microbolometers and difficulty in preparing suspended microbridge structures in planar equiangular spiral antenna structures by designing a planar equiangular spiral antenna structure and adopting a circular pattern design in the etching process.

Description

Technical Field

[0001] The present invention relates to the technical field of terahertz detection, and in particular to a terahertz detector with a planar equiangular spiral antenna structure and a preparation method thereof. Background Art

[0002] The THz band usually refers to electromagnetic waves with a frequency between 0.1THz and 10THz. Its band is between microwaves and infrared light, belonging to the far-infrared band, and has rich physical and chemical information. At the same time, the advantages of THz radiation determine that it can be a complementary technology to Fourier transform infrared spectroscopy technology and X-ray technology in many aspects, making THz electromagnetic waves have quite important applications in many basic research fields, industrial applications and military applications. With the development of THz technology, the application field of THz technology is also constantly expanding. It also has great application potential in biology, medicine, microelectronics, agriculture and other fields.

[0003] Terahertz detection is divided into two categories: coherent detection and incoherent detection. Coherent detection technology converts terahertz signals into low-frequency signals that are easy to detect through nonlinear devices, such as photoconductive antenna sampling method; incoherent detection detects by converting terahertz signals into DC current or voltage signals, such as field effect transistor detectors. The difficulty in terahertz research is that compared with light waves, terahertz photons have low energy (1THz, 4meV), and photonic technology based on electron transitions between quantum energy levels cannot be applied; compared with microwaves and millimeter waves, terahertz wavelengths are short, and micro-manufacturing of devices based on solid-state electronics has reached the process limit. At the same time, its micron-level assembly accuracy poses a huge challenge to mechanical processing and packaging integration. In other words, it is difficult for detectors based on photonics and solid-state electronics principles to obtain high sensitivity and wide bandwidth at 1-10THz. Therefore, for electromagnetic waves above 1 THz, terahertz detectors based on thermal effects have attracted much attention, such as micro-thermal bolometers and pyroelectric detectors. This type of detector based on thermal effects has the advantages of no bandwidth limitation in principle, the preparation process is compatible with silicon-based integrated circuits, and multi-pixel arrays can be obtained.

[0004] However, the sensitivity of these thermal effect detectors is still not high (noise equivalent power is about 10 -10W / √Hz or so). The bow-tie antenna coupled terahertz detector previously developed by the inventor (authorized invention patent ZL202011205369.8) has high sensitivity, but the resonance characteristics of the bow-tie antenna affect the response bandwidth of the detector. The planar equiangular spiral antenna has a small input impedance, and it forms a quasi-optical coupling detector with a super-hemispherical silicon lens to achieve broadband detection. In order to reduce thermal conductivity, the thermal sensitive unit is generally separated from the substrate. Based on the integrated planar equiangular spiral antenna, since the thermal sensitive unit is in the middle of the two arms of the antenna, there are many metal surfaces, which block the etching area. It is very difficult to obtain a suspended microbridge by the conventional method of lateral etching of openings on both sides of the thermal sensitive unit. It is often difficult to etch through the small opening area, or the thermal sensitive unit is etched due to long etching time. Therefore, it brings challenges to the large-scale preparation of terahertz detectors with planar equiangular spiral antenna structures. Summary of the invention

[0005] The purpose of the present invention is to provide a terahertz detector with a planar equiangular spiral antenna structure and a preparation method thereof.

[0006] The technical solution for achieving the purpose of the present invention is: a terahertz detector with a planar equiangular spiral antenna structure, comprising a silicon substrate, a silicon dioxide supporting layer, a hexaniobium nitrogen pentadienide thin film thermal-sensitive layer, and a planar equiangular spiral antenna electrode layer, wherein the silicon dioxide supporting layer is grown on the silicon substrate; the hexaniobium nitrogen pentadienide thin film thermal-sensitive layer is grown on the silicon dioxide supporting layer, and the silicon dioxide supporting layer and the silicon substrate are photolithographically and etched by designing a circular etching window to form a hexaniobium nitrogen pentadienide microbridge suspended structure; the planar equiangular spiral antenna electrode layer also serves as a coupling antenna, and is located on the hexaniobium nitrogen pentadienide thin film thermal-sensitive layer, and the central feeding structure of the planar equiangular spiral antenna is directly connected to the two ends of the hexaniobium nitrogen pentadienide microbridge.

[0007] Furthermore, the planar equiangular spiral antenna electrode layer adopts a self-complementary planar equiangular spiral antenna, the antenna part and the air gap part have the same size, and the number of spiral turns is controlled to be 1.5 to 2 turns.

[0008] Furthermore, the distance between the two ends of the antenna of the center feed structure and the outer diameter of the antenna are determined by the desired antenna operating frequency. The lower limit frequency f L Determined by the overall radius R of the antenna, the specific calculation relationship is: Upper limit operating frequency f H It is determined by the distance r0 between the two ends of the feeding center. The specific calculation formula is: Where c is the speed of light.

[0009] Furthermore, the distance between the two ends of the antenna of the center feed structure is controlled to be 4 to 12 microns, the width of the antenna at the center of the center feed is controlled to be 2 to 4 microns, and the overall radius of the antenna is controlled to be 50 to 150 microns.

[0010] Furthermore, the length of the hexanitride pentanibium microbridge is designed to be 6 to 12 microns, and the width is designed to be 2 to 4 microns.

[0011] Furthermore, the center of the circular etching window coincides with the center of the planar equiangular spiral antenna, the inner diameter of the circular ring is adjusted according to the size of the hexanitride pentadienium microbridge, the distance between the inner radius and the hexanitride pentadienium microbridge is controlled to be 2 to 5 microns, and the outer radius is adjusted according to the overall antenna size and is controlled to be 1 / 10 to 1 / 5 of the overall antenna radius.

[0012] A method for preparing a terahertz detector with a planar equiangular spiral antenna structure, for preparing the terahertz detector with a planar equiangular spiral antenna structure, comprises the following steps:

[0013] Step 1, growing a hexanitride pentaniobium thin film thermal sensitive layer on a silicon dioxide support layer by magnetron sputtering;

[0014] Step 2, peeling off the electrode and antenna patterns on the thermosensitive layer of the hexanitride pentaniobium film by photolithography growth;

[0015] Step 3, photolithography of a hexanitride-pentadienium niobium microbridge pattern, and forming a hexanitride-pentadienium niobium microbridge by reactive ion etching;

[0016] Step 4, exposing a circular etching window around the hexanitride 5-niobium microbridge by photolithography, and etching the silicon dioxide support layer and the silicon substrate by reactive ion etching to form a hexanitride 5-niobium microbridge suspended structure.

[0017] Compared with the prior art, the present invention has the following significant advantages: 1) the planar equiangular spiral antenna adopts a self-complementary structure to achieve wide-band detection of terahertz waves; 2) the shape of the etching pattern is set to a circular ring, and a suspended microbridge is formed by etching the circular ring area, which solves the problem that the suspended bridge structure cannot be prepared due to the small etching area caused by excessive metal in the planar equiangular spiral antenna. The preparation process is stable and suitable for large-scale array preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a planar equiangular spiral antenna shape graphic.

[0019] Figure 2 This is the graphic of the integration of the planar equiangular spiral antenna and the hexanitride pentaniobium thin film.

[0020] Figure 3 This is a simulation diagram of the transmission characteristics of the plane equiangular spiral antenna port.

[0021] Figure 4 Schematic diagram of the detector preparation process

[0022] Figure 5 Schematic diagram of the etching ring area designed for etching the suspended microbridge of the present invention

[0023] Figure 6 This is an optical microscope magnified image of the planar equiangular spiral antenna terahertz detector prepared by the present invention, wherein Figure (a) is the overall image of the device, and Figure (b) is a further magnified image. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0025] The present invention solves the problems of low detection bandwidth of conventional hexanitrogen pentaniobium terahertz microbolometer and difficult preparation of suspended microbridge structure in the planar equiangular spiral antenna structure by designing a planar equiangular spiral antenna structure and adopting a circular ring pattern design in the etching process.

[0026] like Figure 1 , 2 As shown, a terahertz detector with a planar equiangular spiral antenna structure includes a silicon substrate, a silicon dioxide supporting layer, a hexanitrogen pentadienium thermosensitive film layer, and an electrode antenna layer. The silicon dioxide supporting layer is grown on the silicon substrate, and the hexanitrogen pentadienium thermosensitive film layer is grown on the silicon dioxide supporting layer. A hexanitrogen pentadienium thin film microbridge suspended structure is formed by etching. The electrode layer also serves as a coupling antenna, which is a planar equiangular spiral antenna structure and is located on the hexanitrogen pentadienium thin film thermosensitive layer. The central feeding structure of the planar equiangular spiral antenna is directly connected to both ends of the hexanitrogen pentadienium microbridge.

[0027] The planar equiangular helical antenna is a self-complementary helical antenna, that is, the antenna part and the air gap part are completely consistent, the helical degree is controlled to be 540° to 720°, and the lower limit frequency f of its operation is L Determined by the overall radius R of the antenna, the specific calculation relationship is shown in formula 1: (where c is the speed of light), the upper limit operating frequency f H It is determined by the distance r0 between the two ends of the feeding center. The specific calculation formula is shown in Formula 2: (where c is the speed of light). In order to enable the device to reach the terahertz band that needs to be detected, the distance between the two ends of the antenna at the center feed center is controlled to 4 to 12 microns, the antenna width at the center feed center is controlled to 2 to 4 microns, and the overall radius of the antenna is controlled to 50 to 150 microns.

[0028] The length of the niobium hexanitride pentazoline film is designed to be 6 to 12 microns, and the width is designed to be 2 to 4 microns, so as to achieve impedance matching between the niobium hexanitride pentazoline film microbridge and the planar antenna.

[0029] The hexanitrogen pentaniobium film microbridge suspended structure is realized by photolithography and etching of a silicon dioxide support layer and a silicon substrate to form an air cavity, and the steps are as follows:

[0030] 1. Set the shape of the etched pattern to a ring, the center of the ring coincides with the center of the spiral antenna, the inner diameter of the ring is adjusted according to the size of the film, the distance between the inner radius and the film is controlled to be 2 to 5 microns, and the outer radius is adjusted according to the overall antenna size and controlled to be 1 / 10 to 1 / 5 of the overall antenna radius;

[0031] 2. Through ultraviolet lithography, a circular ring area is exposed around the microbridge of the hexanitride pentaniobium film for subsequent etching process;

[0032] 3. The silicon in the annular area is etched by reactive ion etching (RIE) to form a suspended microbridge of the hexanitride pentaniobium film through lateral etching.

[0033] The present invention also proposes a method for preparing a terahertz detector, which realizes the preparation of a terahertz detector based on a planar equiangular spiral antenna structure. Figure 4 As shown, the following steps are included:

[0034] Step 1: To improve device performance, the device should be insulated from the outside world as much as possible during operation to reduce heat loss. Therefore, the present invention selects SiO2 with a small thermal conductivity as the support layer of the microbridge, and grows a hexanitride pentaniobium thin film thermal sensitive layer on the silicon dioxide support layer by magnetron sputtering;

[0035] Step 2, peeling off the antenna pattern on the thermosensitive layer of the hexanitride pentaniobium film by photolithography growth;

[0036] Step 3, photolithography of a hexanitride-pentadienium niobium microbridge pattern, and forming a hexanitride-pentadienium niobium microbridge by reactive ion etching;

[0037] Step 4, exposing a circular window around the hexanitride 5-niobium microbridge by photolithography, and etching the silicon dioxide support layer and the silicon substrate by reactive ion etching to form a hexanitride 5-niobium microbridge suspended structure.

[0038] Example

[0039] In order to verify the effectiveness of the solution of the present invention, the following experiment was conducted.

[0040] In this embodiment, the overall radius of the antenna is determined to be 100 microns, the distance between the two ends of the center-fed center antenna is 6 microns, the width of the feed center antenna is 3 microns, the length and width of the hexaniobium pentadienide film microbridge are 6 microns and 3 microns respectively, and after the planar equiangular spiral antenna and the hexaniobium pentadienide film are integrated, as shown in FIG. Figure 2 The planar equiangular spiral antenna is a non-frequency-variable antenna. The antenna impedance of the self-complementary structure is 188.5Ω. Its port transmission characteristics are shown in Figure 3As shown, at 0.25THz~3.5THz, the reflection coefficient S 11 Basically, it can reach -10dB.

[0041] The preparation method of a terahertz broadband detector with a planar equiangular spiral antenna structure, the process steps are as follows Figure 4 As shown, including:

[0042] (1) SiO2 with a small thermal conductivity coefficient is selected as the support layer of the microbridge, and the silicon wafer is thermally oxidized to generate 220nm SiO2 on the surface;

[0043] (2) The double-layer substrate was ultrasonically cleaned in acetone, alcohol and deionized water for 10 minutes, and the surface of the substrate was blown clean with a N2 air gun for later use;

[0044] (3) Magnetron sputtering was performed on a double-layer substrate of Si and SiO2 to grow a 120 nm hexanitride pentaniobium thermal sensitive film. The specific growth steps and process are as follows:

[0045] a. First, the substrate is ion milled to remove molecular-level impurities on the substrate surface to make the film grow evenly. The specific ion milling process conditions are shown in Table 1.

[0046] Table 1: Ion milling conditions

[0047] Gas Type Gas flow Working air pressure Ion beam current Cleaning time Ar 10sccm 300V 30mA 1min

[0048] b. The ion-milled substrate is sent into the main chamber to grow the Nb5N6 film by magnetron sputtering. The specific process conditions are shown in Table 2.

[0049] Table 2: Magnetron sputtering growth conditions of niobium hexanitride pentaoxide thin films

[0050]

[0051] (4) After sputtering, the sample was taken out and LOR10B and AZ1500 photoresists were spin-coated on the sample surface. The sample was exposed for 4 seconds using a photolithography machine, developed for 14 seconds, and fixed in deionized water for two minutes. The specific photolithography conditions are shown in Table 3.

[0052] Table 3: Photolithography conditions

[0053]

[0054] (5) After photolithography and development, the sample is sent to a magnetron sputtering system for ion milling. The ion milling process is the same as step 3(a). Then, a gold film is grown by sputtering. The conditions for DC sputtering to grow the gold film are shown in Table 4.

[0055] Table 4: Process conditions for DC sputtering of gold thin films

[0056] Target Gas Type Gas flow Sputtering pressure Sputtering power Sputtering time gold Ar 100sccm 4mTorr 80W 100s

[0057] (6) Use ultrasound to peel off the gold electrodes and antenna.

[0058] (7) Photolithography is performed again. First, AZ1500 is spin-coated and dried. This time, LOR10B does not need to be spin-coated. The process is the same as step 4. After photolithography and development, the hexanitride pentadienium microbridge pattern is obtained. Then, the excess hexanitride pentadienium film is removed by etching in a reactive ion etcher (RIE). The specific etching conditions are shown in Table 5.

[0059] Table 5: Process conditions for reactive ion etching of hexanitrogen pentaniobium microbridges

[0060] Etched material Reaction gas Gas flow Etching pressure Etching power Etching time <![CDATA[Nb5N6]]> <![CDATA[SF6]]> 40sccm 4Pa 100W 60s

[0061] (8) After etching to form the hexanitride pentadienium microbridge pattern, the residual glue is removed using acetone, alcohol, and water in sequence.

[0062] (9) Spin-coat a layer of AZ601 photoresist on the sample, dry it, and then perform photolithography exposure to draw the pattern of etching the air cavity. Considering that the planar equiangular spiral antenna is circular and the antenna part overlaps with the air gap part, the etching window is designed as a ring, such as Figure 5 As shown, the size of the ring is that the inner radius and the distance between the microbridge are 4 microns, and the outer radius is 15 microns. The specific photolithography development conditions are shown in Table 6.

[0063] Table 6: AZ601 coating, exposure and development conditions

[0064]

[0065] (10) After the sample is exposed and developed, it is placed in RIE for etching. First, the silicon oxide layer at the window is etched away, and then the silicon substrate underneath is etched until the silicon substrate under the hexanitride pentaniobium nanobridge is etched through to form an air cavity. The specific etching parameters are shown in Table 7.

[0066] Table 7: Process conditions for reactive ion etching of air chambers

[0067] Etched material Reaction gas Gas flow Etching pressure Etching power Etching time <![CDATA[SiO2]]> <![CDATA[CF4 / O2]]> 30 / 10sccm 4Pa 150W 3min Si <![CDATA[SF6]]> 30sccm 8Pa 70W 12min

[0068] (11) After etching, the sample was sequentially passed through acetone, alcohol, and water to remove the residual glue, and then dried to obtain Figure 6 The figures shown, wherein Figure (a) is the overall figure of the device under an optical microscope, and Figure (b) is a further enlarged figure.

[0069] In summary, the planar equiangular spiral antenna terahertz detector prepared based on the process of the present invention adopts a planar equiangular spiral antenna structure and a special photolithography ring etching method to suspend the membrane, thereby obtaining a wide-band terahertz detector with stable process and simple implementation.

[0070] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0071] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A terahertz detector with a planar equiangular spiral antenna structure, characterized in that: It comprises a silicon substrate, a silicon dioxide support layer, a hexaniobium pentadienide thin film thermal-sensitive layer, and a planar equiangular spiral antenna electrode layer, wherein the silicon dioxide support layer is grown on the silicon substrate; the hexaniobium pentadienide thin film thermal-sensitive layer is grown on the silicon dioxide support layer, and the silicon dioxide support layer and the silicon substrate are photolithographically and etched by designing a circular etching window to form a hexaniobium pentadienide microbridge suspended structure; the planar equiangular spiral antenna electrode layer also serves as a coupling antenna, and is located on the hexaniobium pentadienide thin film thermal-sensitive layer, and the central feeding structure of the planar equiangular spiral antenna is directly connected to both ends of the hexaniobium pentadienide microbridge; The distance between the two ends of the antenna of the center feed structure and the outer diameter of the antenna are determined by the desired antenna operating frequency. The lower limit frequency f L Determined by the overall radius R of the antenna, the specific calculation relationship is: Upper limit operating frequency f H It is determined by the distance r0 between the two ends of the feeding center. The specific calculation formula is: Where c is the speed of light.

2. The terahertz detector with a planar equiangular spiral antenna structure according to claim 1, characterized in that: The planar equiangular spiral antenna electrode layer adopts a self-complementary planar equiangular spiral antenna, the antenna part and the air gap part have the same size, and the number of spiral turns is controlled to be 1.5 to 2 turns.

3. The terahertz detector with a planar equiangular spiral antenna structure according to claim 1, characterized in that: The distance between the two ends of the antenna of the center feed structure is controlled to be 4 to 12 microns, the antenna width at the center of the center feed is controlled to be 2 to 4 microns, and the overall radius of the antenna is controlled to be 50 to 150 microns.

4. The terahertz detector with a planar equiangular spiral antenna structure according to claim 1, characterized in that: The length of the hexanitrogen pentadienium microbridge is designed to be 6 to 12 microns, and the width is designed to be 2 to 4 microns.

5. The terahertz detector with a planar equiangular spiral antenna structure according to claim 1, characterized in that: The center of the circular etching window coincides with the center of the planar equiangular spiral antenna, the inner diameter of the circular ring is adjusted according to the size of the hexanitride pentadienium microbridge, the distance between the inner radius and the hexanitride pentadienium microbridge is controlled to be 2 to 5 microns, and the outer radius is adjusted according to the overall radius size of the antenna and is controlled to be 1 / 10 to 1 / 5 of the overall radius of the antenna.

6. A method for preparing a terahertz detector with a planar equiangular spiral antenna structure, used for preparing a terahertz detector with a planar equiangular spiral antenna structure as claimed in any one of claims 1 to 5, characterized in that: The steps include: Step 1, growing a thermosensitive layer of hexanitride pentaniobium thin film on a silicon dioxide support layer by magnetron sputtering; Step 2, peeling off the antenna pattern on the thermosensitive layer of the hexanitride pentaniobium film by photolithography growth; Step 3, photolithography of a hexanitride-pentadienium niobium microbridge pattern, and forming a hexanitride-pentadienium niobium microbridge by reactive ion etching; Step 4, exposing a circular etching window around the hexanitride 5-niobium microbridge by photolithography, and etching the silicon dioxide support layer and the silicon substrate by reactive ion etching to form a hexanitride 5-niobium microbridge suspended structure.

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