Optically controlled radio frequency switch based on zinc oxide nanowire array

Abstract

The application relates to a photo-controlled radio frequency switch based on zinc oxide nanowire arrays, and relates to the fields of nanotechnology and radio frequency technology. The structure is as follows: a radio frequency switch is prepared on a selected substrate, each switch structure comprises two opposite zinc oxide seed layers, a longitudinal nanowire inhibition layer is arranged above the seed layers, and a composite electrode layer is arranged above the inhibition layer in a staggered mode. Zinc oxide nanowires of a photosensitive part grow on the sidewalls of the seed layers, and the nanowires on both sides of the gap form a bridge. According to the impedance change caused by the width change of the depletion layer of the zinc oxide nanowires before and after ultraviolet light irradiation, the opening and closing states of the switch are controlled. The radio frequency switch is prepared at the nanometer level, the demand of miniaturization of radio frequency devices and photoelectric conversion devices can be met, zinc oxide has multiple nano structures, the preparation process is relatively simple, large-scale production is suitable, the cost is lower, and a radio frequency switch matrix can be realized.

Description

TECHNICAL FIELD

[0001] The application relates to the field of nanotechnology and radio frequency technology, and particularly relates to a light-controlled radio frequency switch based on a zinc oxide nanowire array. BACKGROUND

[0002] With the rapid development of information technology, wireless communication, military, satellite communication and other high-frequency and high-temperature fields have put forward more requirements for small-size and light-weight radio frequency devices. The radio frequency switch is a key element in the radio frequency device, which can not only ensure that the radio frequency tag, Bluetooth and other devices support multi-band operation, but also affect the radiation direction and resonant frequency of the antenna in the reconfigurable antenna. At present, the conventional radio frequency switch is millimeter level, and the technologies adopted include diodes and micro-electromechanical systems. However, with the miniaturization of radio frequency devices, the conventional radio frequency switch process cannot meet the needs of new devices. Nanoelectronic devices have attracted widespread attention, and with the device size being reduced to the nanoscale, some new properties such as surface effect and quantum size effect are brought about, which promote the application research of nanodevices in the radio frequency field.

[0003] Zinc oxide is an important II-IV group direct band gap wide band gap semiconductor material, and in the past few years, it has become a hot spot in the research of semiconductor materials due to its excellent performance. When the size of zinc oxide reaches the nanoscale, many new properties such as piezoelectric properties and near-ultraviolet emission are brought about. Based on this, zinc oxide nanomaterials have been widely used in the fields of piezoelectricity, ultraviolet detectors and gas sensors. When the zinc oxide nanowire is used as an ultraviolet detector, the surface depletion layer of the nanowire changes before and after ultraviolet light irradiation, thereby affecting the impedance size. When the zinc oxide nanowire is used as a gas detector, the detected gas molecules will cause electron transfer with the nanowire, affect the surface depletion layer and finally affect the impedance change of the nanowire. The above-mentioned detectors are based on the impedance change of the nanowire for detection, but are in the direct current condition. In 2012, it was reported that a single zinc oxide nanowire has the characteristics of microwave transmission measured by the transfer method, which has proved the potential of zinc oxide nanowire in the radio frequency field. The existing InAs nanowire radio frequency switch based on the coplanar waveguide is realized by controlling the impedance change of the InAs nanowire through the gate voltage, but the preparation method of the InAs nanowire is complicated, and the nanowire needs to be placed in the switch part through the nanowire transfer, which leads to uneven distribution of the nanowire and is not suitable for large-scale radio frequency switch matrix, and the application scene is limited. Zinc oxide has various nanostructures, and the preparation process is simple, the growth of the nanowire can be controlled, and a uniform nanowire array can be prepared to realize the radio frequency switch matrix. The sensitivity of zinc oxide also makes its application in the radio frequency field more flexible and diverse. SUMMARY

[0004] In view of the above, the present application aims to provide a zinc oxide nanowire array-based light-controlled radio frequency switch, which utilizes the sensitivity of zinc oxide nanowires to control the opening and closing states of the switch according to the impedance change caused by the width change of the depletion layer on the surface of zinc oxide nanowires before and after ultraviolet light irradiation; under the condition of no light and air, a high-resistance depletion layer is formed on the surface of zinc oxide nanowires, at this time, the nanowire impedance is large, and the transmission coefficient of radio frequency signals transmitted through the nanowire is low; when ultraviolet light irradiation occurs, the electron-hole pairs of zinc oxide nanowires are separated, the depletion layer is thinned, the conductive channel is opened, and the internal electron carrier concentration of the nanowire is increased, at this time, the nanowire is in a low-resistance state, and the radio frequency signals transmitted along the nanowire are enhanced.

[0005] A zinc oxide nanowire array-based light-controlled radio frequency switch, comprising: a substrate, a zinc oxide seed layer, a longitudinal nanowire inhibition layer, a composite electrode layer, and zinc oxide nanowires; there are at least two parallel zinc oxide seed layers (4) on the substrate (3), and the two zinc oxide seed layers have a gap therebetween, and the opposite sides of the two zinc oxide seed layers are referred to as A sides; the upper surfaces of the two zinc oxide seed layers are longitudinal nanowire inhibition layers (2), and the composite electrode layer (1) covers the longitudinal nanowire inhibition layer (2) and the zinc oxide seed layer (4), but only the A side of the zinc oxide seed layer, the A side of the longitudinal nanowire inhibition layer (2), and the upper surface adjacent to the A side of the longitudinal nanowire inhibition layer are exposed, the A side of the zinc oxide seed layer has a transversely grown ZnO nanowire array, the ZnO nanowires (5) in the ZnO nanowire array on the A side of the two zinc oxide seed layers are connected together to form a bridging structure, and the bridging structure is suspended between the two composite electrode layers (1).

[0006] Preferably, the width of the zinc oxide seed layer is 3-5 microns, the thickness of the zinc oxide seed layer is 90-150 nanometers, and the width of the gap between the two zinc oxide seed layers is determined according to requirements;

[0007] Preferably, the longitudinal nanowire inhibition layer (2) has a Ti layer and an Au layer in sequence from the zinc oxide seed layer (4) upwards, i.e., the thickness of the Ti layer is 3-6 nanometers, and the thickness of the Au layer is 10-20 nanometers;

[0008] Preferably, the composite electrode layer has a Ti layer and an Au layer in sequence from the longitudinal nanowire inhibition layer (2) outwards, i.e., the thickness of the Ti layer is 10-20 nanometers, and the thickness of the Au layer is 500-1200 nanometers;

[0009] The diameter of the ZnO nanowire is 50-300 nanometers, and the length of the ZnO nanowire is determined according to the distance between the two ZnO seed layers;

[0010] A method for using a photo-controlled radio frequency switch based on zinc oxide nanowire array: by using the sensitivity of zinc oxide nanowire, a high-resistance depletion layer is formed on the surface of zinc oxide nanowire under the condition of no light and air, and the zinc oxide at the bridging position of the bridging structure is equivalent to being disconnected, at this time, the impedance of the nanowire bridging structure is relatively large, and the transmission coefficient of the radio frequency signal transmitted through the nanowire is relatively low; when ultraviolet light is irradiated, the electron-hole pairs of the zinc oxide nanowire are separated, the depletion layer is thinned, the zinc oxide at the bridging position is bridged together, which is equivalent to the opening of the conductive channel, and the concentration of the electron carriers in the nanowire is increased, at this time, the nanowire is in a low-resistance state, and the radio frequency signal transmitted along the nanowire is enhanced.

[0011] The wavelength of the ultraviolet light is 10-400 nm, and the light intensity is greater than 1 mw / cm 2 .

[0012] A preparation method of a photo-controlled radio frequency switch based on zinc oxide nanowire array, comprising the following steps:

[0013] Step 1: clean the used substrate material and dry it;

[0014] Step 2: spin-coat photoresist, and pattern the substrate by using a photoetching process;

[0015] Step 3: on the patterned substrate, sputter ZnO thin film and longitudinal nanowire inhibition layer in sequence by using a radio frequency magnetron sputtering method;

[0016] Step 4: peel off the photoresist by using a peeling process, and clean the sample after peeling off, so as to leave the seed layer and the longitudinal nanowire inhibition layer;

[0017] Step 5: spin-coat photoresist on the cleaned sample in step 4 again, perform secondary photoetching, and pattern the sample again;

[0018] Step 6: sputter Ti / Au electrode layer on the sample after photoetching in step 5 by using a radio frequency magnetron sputtering method;

[0019] Step 7: peel off the photoresist by using a peeling process, so as to leave the seed layer, the longitudinal nanowire inhibition layer and the metal electrode;

[0020] Step 8: place the sample with the sputtered material on the side facing down, so that the sample floats in the prepared precursor solution in advance, and grow the horizontal ZnO nanowire array on the side wall of the ZnO thin film by using a hydrothermal method;

[0021] In the application, the precursor solution used in the hydrothermal method is composed of zinc nitrate hexahydrate and hexamethylenetetramine. The molar ratio of the zinc salt and the hexamethylenetetramine is preferably 1:1-1:2, and the concentration of the zinc salt is preferably 0.5-1.5 mmol / L.

[0022] In the present application, the temperature of the hydrothermal reaction is preferably 70-90 DEG C, and the time of the hydrothermal reaction is preferably 10-32 hours.

[0023] The present application does not have special requirements for the specific operation methods and conditions of the photolithography, radio frequency magnetron sputtering and stripping used in the above-mentioned scheme, and the operation methods and conditions well known to those skilled in the art can be used.

[0024] The present application reduces the nanowire transfer process and simplifies the process steps by forming a conductive channel between two electrodes by self-organizing growth of the lateral nanowire, and avoids affecting the nanowire in the transfer process.

[0025] According to the principle provided by the present application, the present application provides a photo-controlled radio frequency switch based on a zinc oxide nanowire array, comprising: a substrate, a zinc oxide seed layer, a longitudinal nanowire inhibition layer, a composite electrode layer, and zinc oxide nanowires, wherein the zinc oxide seed layer is on the substrate, the longitudinal nanowire inhibition layer is on the zinc oxide seed layer, and the composite electrode layer is on the longitudinal nanowire inhibition layer. In the absence of light, a high-resistance depletion layer is formed on the surface of the zinc oxide nanowires, and at this time the transmission coefficient of the radio frequency signal in the nanowires is low; when ultraviolet light is irradiated, the electron-hole pairs of the zinc oxide nanowires are separated, the depletion layer is thinned, the conductive channel is opened, and the electron carrier concentration in the nanowires is increased, at this time the nanowires are in a low-resistance state, and the transmission of the radio frequency signal in the nanowires is enhanced; and the photo-controlled radio frequency switch is realized according to the above. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 A cross-sectional view of the switch part of the present application;

[0027] Figure 2 A schematic diagram of the nanowire surface depletion layer of the nanowire in the present application under the absence of ultraviolet light irradiation;

[0028] Figure 3 A schematic diagram of the nanowire surface depletion layer of the nanowire in the present application under ultraviolet light irradiation;

[0029] Figure 4A The S11 curves measured before and after ultraviolet light irradiation in Example 1 of the present application;

[0030] Figure 4B The S21 curves measured before and after ultraviolet light irradiation in Example 1 of the present application.

[0031] In the figure: 1, composite electrode layer; 2, longitudinal nanowire inhibition layer; 3, substrate; 4, zinc oxide seed layer; 5, nanowire; 6, nanowire surface depletion layer; 7, conductive channel; 8, ultraviolet light irradiation with a wavelength of 365 nm. DETAILED DESCRIPTION

[0032] The application will be further described by the following examples. However, this should not be understood as limiting the scope of the above-mentioned subject matter of the application to the following examples.

[0033] Example 1

[0034] This example provides a zinc oxide nanowire array-based light-controlled radio frequency switch, the specific structure is shown in Figure 1 , and the use is shown in Figures 2-3 .

[0035] The radio frequency switch comprises a substrate, a zinc oxide seed layer, a longitudinal nanowire inhibition layer, a composite electrode, and a zinc oxide nanowire. In the absence of light, oxygen molecules are adsorbed on the surface of the zinc oxide nanowire to form ionic adsorbed oxygen, and a high-resistance depletion layer is formed nearby. At this time, the nanowire impedance is large, and the transmission coefficient of the radio frequency signal transmitted through the nanowire is small. When ultraviolet light is irradiated, the electron-hole pairs of the zinc oxide nanowire are separated, the ionic adsorbed oxygen on the surface of the nanowire captures holes, and the adsorbed oxygen molecules are desorbed. At this time, the nanowire is in a low resistance state, and the radio frequency signal along the nanowire is enhanced.

[0036] The specific process steps of Example 1 of the application are as follows:

[0037] Step 1: Select a common glass with a thickness of 500 um as a substrate, and clean the substrate with acetone, ethanol and deionized water in sequence. After cleaning, dry the substrate with a nitrogen gun, and then dry it in an oven;

[0038] Step 2: Spin-coat photoresist on the substrate in step 1, and pattern the substrate by using a photolithography process;

[0039] Step 3: Sputter a 150-nanometer-thick ZnO seed layer on the patterned substrate in step 2 by using a radio frequency magnetron sputtering method, with a width of 5 micrometers, a length of 100 micrometers, and a distance between the two seed layers of 5 micrometers;

[0040] Step 4: Sputter a longitudinal nanowire inhibition layer by using a radio frequency magnetron sputtering method, with a Ti thickness of 5 nanometers and an Au thickness of 15 nanometers;

[0041] Step 5: Strip the photoresist by using a stripping process, and clean the sample after stripping to leave the seed layer and the longitudinal nanowire inhibition layer;

[0042] Step 6: Dry the cleaned sample in step 5, spin-coat photoresist, and pattern the substrate again by using a photolithography process;

[0043] Step 7: Sputter a composite electrode layer on the sample in step 6 by using a radio frequency magnetron sputtering method, with a Ti thickness of 15 nanometers and an Au thickness of 600 nanometers;

[0044] Step 8, the photoresist is stripped by a stripping process, and the sample is cleaned after stripping, leaving the seed layer, the longitudinal nanowire inhibition layer and the composite electrode;

[0045] Step 9, 1 mmol of Zn(NO3)2·6H2O and 1 mmol of hexamethylenetetramine are dissolved in 1 L of deionized water, stirred for 2 hours, as a precursor solution for nanowire growth; 250 mL of the precursor solution is taken into a hydrothermal reaction kettle, and the sample is placed with the patterned side downward, so as to float in the precursor solution, and grown at 80℃ for 16 h; the sample with grown ZnO nanowires is washed with a large amount of deionized water, and then dried with nitrogen.

Claims

1. A photo-controlled radio frequency switch based on zinc oxide nanowire array, characterized in that, Comprise: Substrate, zinc oxide seed layer, longitudinal nanowire inhibition layer, composite electrode layer, zinc oxide nanowire; There are at least two parallel zinc oxide seed layer (4) on the substrate (3), there is a gap between the two zinc oxide seed layer, the opposite side of the two zinc oxide seed layer is called A side; the upper surface of the two zinc oxide seed layer is longitudinal nanowire inhibition layer (2), composite electrode layer (1) covers longitudinal nanowire inhibition layer (2) and zinc oxide seed layer (4), but only the A side of zinc oxide seed layer, the A side of longitudinal nanowire inhibition layer (2) and the upper surface adjacent to the A side of longitudinal nanowire inhibition layer are exposed, the A side of zinc oxide seed layer has transverse growth of ZnO nanowire array, the ZnO nanowire (5) in the ZnO nanowire array of the A side of the two zinc oxide seed layer is connected together, forming a bridge structure, hanging between the two composite electrode layer (1); The width of zinc oxide seed layer is 3-5 microns, and the thickness of zinc oxide seed layer is 90-150 nanometers; The longitudinal nanowire inhibition layer (2) is Ti layer and Au layer in turn from the zinc oxide seed layer (4), that is, the thickness of Ti layer is 3-6 nanometers, and the thickness of Au layer is 10-20 nanometers; The composite electrode layer is Ti layer and Au layer in turn from the longitudinal nanowire inhibition layer (2), that is, the thickness of Ti layer is 10-20 nanometers, and the thickness of Au layer is 500-1200 nanometers; The diameter of ZnO nanowire is 50-300 nanometers; The sensitivity of zinc oxide nanowire is used, under the condition of no light and air, the high resistance depletion layer is formed on the surface of zinc oxide nanowire, the zinc oxide of the bridge connection of the bridge structure is equivalent to be disconnected, at this time, the impedance of the nanowire bridge structure is large, and the transmission coefficient of the radio frequency signal is low when the radio frequency signal is transmitted through the nanowire; When the ultraviolet light is irradiated, the electron hole pair of zinc oxide nanowire is separated, the depletion layer is thinned, the zinc oxide of the bridge connection is connected together, which is equivalent to the opening of the conductive channel, and the electron carrier concentration in the nanowire is increased, at this time, the nanowire is in low resistance state, and the radio frequency signal along the nanowire is enhanced; The wavelength of the ultraviolet light is 10-400 nm, and the light intensity is greater than 1 mw / cm 2 .

2. The method for fabricating a light-controlled radio frequency switch based on a zinc oxide nanowire array as described in claim 1, characterized in that, The method comprises the following steps: Step 1: clean the substrate material used and dry it; Step 2: spin coating photoresist, and using photoetching process to pattern the substrate; Step 3: on the patterned substrate, ZnO film and longitudinal nanowire inhibition layer are sputtered in turn by radio frequency magnetron sputtering; Step 4: the photoresist is stripped by stripping process, and after stripping, the sample is cleaned, leaving the seed layer and longitudinal nanowire inhibition layer; Step 5: the sample cleaned in step 4 is spin coated with photoresist again, and the sample is patterned again by second photoetching; Step 6: the sample after photoetching in step 5 is sputtered with Ti / Au electrode layer by radio frequency magnetron sputtering; Step 7: the photoresist is stripped by stripping process, leaving the seed layer, longitudinal nanowire inhibition layer and metal electrode; Step 8: the side of the sample sputtered with material is downward, and the sample is floated in the prepared precursor solution, and the transverse ZnO nanowire array is grown on the side wall of ZnO film by hydrothermal method.

3. The method of claim 2, wherein, The precursor solution used in the hydrothermal method is composed of zinc nitrate hexahydrate and hexamethylenetetramine; the molar ratio of zinc nitrate hexahydrate to hexamethylenetetramine is 1:1-1:2; the concentration of zinc salt is 0.5-1.5 mmol / L.

4. The method of claim 3, wherein, The temperature of the hydrothermal reaction is 70-90 DEG C; the time of the hydrothermal reaction is 10-32 hours.

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