CN116760382A - Reconfigurable SAW resonator structure and preparation method - Google Patents
Reconfigurable SAW resonator structure and preparation method Download PDFInfo
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- CN116760382A CN116760382A CN202310658269.8A CN202310658269A CN116760382A CN 116760382 A CN116760382 A CN 116760382A CN 202310658269 A CN202310658269 A CN 202310658269A CN 116760382 A CN116760382 A CN 116760382A
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- 238000002360 preparation method Methods 0.000 title abstract description 12
- AJNVQOSZGJRYEI-UHFFFAOYSA-N digallium;oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[Ga+3].[Ga+3] AJNVQOSZGJRYEI-UHFFFAOYSA-N 0.000 claims abstract description 28
- 229910001195 gallium oxide Inorganic materials 0.000 claims abstract description 28
- 150000002500 ions Chemical class 0.000 claims abstract description 18
- 238000000034 method Methods 0.000 claims abstract description 16
- 238000004519 manufacturing process Methods 0.000 claims abstract description 12
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- -1 fluoride ions Chemical class 0.000 claims description 4
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Classifications
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/02—Details
- H03H9/02535—Details of surface acoustic wave devices
- H03H9/02543—Characteristics of substrate, e.g. cutting angles
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H3/00—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
- H03H3/007—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks
- H03H3/08—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of resonators or networks using surface acoustic waves
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/02—Details
- H03H9/125—Driving means, e.g. electrodes, coils
- H03H9/13—Driving means, e.g. electrodes, coils for networks consisting of piezoelectric or electrostrictive materials
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/02—Details
- H03H9/125—Driving means, e.g. electrodes, coils
- H03H9/145—Driving means, e.g. electrodes, coils for networks using surface acoustic waves
Abstract
The invention discloses a reconfigurable SAW resonator structure and a preparation method thereof, relates to a new generation of information technology, and provides a scheme for solving the problems of high thickness, low carrier concentration, high direct current bias voltage and large leakage current in the prior art. The SAW resonator structure mainly comprises a conductive layer which is obtained by injecting negative ions into the upper end part of an epsilon-phase gallium oxide piezoelectric film; a dielectric layer and a pair of interdigital electrodes are arranged on the conductive layer; one interdigital electrode is respectively connected with a direct-current bias voltage and an RF signal, and the other interdigital electrode is grounded. The method is mainly to inject negative ions into the surface of the epsilon-phase gallium oxide piezoelectric film to form a conductive layer at the upper end of the epsilon-phase gallium oxide piezoelectric film. The method has the advantages that the thickness is not limited after the concentration of the carriers is increased, and the design and the manufacture are more flexible and simple. The high-concentration two-dimensional electron gas is more sensitive to the change of direct current bias voltage, and can be adjusted only by lower voltage. After the insulating dielectric layer is introduced, no leakage current exists, and the problem of large heating value is avoided.
Description
Technical Field
The invention relates to a reconfigurable SAW resonator structure and a preparation method thereof.
Background
The surface acoustic wave (Surface Acoustic Wave, SAW) resonator has excellent characteristics of high operating frequency, high quality factor (Q), high stability, low insertion loss, compact volume and the like, and can be used for preparing devices such as filters, sensors and the like. The SAW resonator-based filter device has advantages of low manufacturing cost, small size, light weight, high reliability, and the like, which are incomparable with other types of filters, and has been widely used in mobile communication systems.
The core component of the SAW resonator includes interdigital electrodes (Inter Digital Transducer, IDT) and a piezoelectric substrate arranged in pairs. Wherein the IDT is a finger electrode arranged on the surface of the piezoelectric substrate, and two adjacent fingers are respectively grounded and connected with RF signals. The SAW resonator operates on the principle that when an RF signal is applied to the interdigital electrodes, an alternating electric field acts on the piezoelectric substrate and produces mechanical vibrations by the inverse piezoelectric effect, thereby exciting an elastic wave propagating along the surface of the piezoelectric substrate. When the frequency of the applied signal is consistent with the characteristic frequency of the mechanical vibration of the piezoelectric substrate, the formed elastic wave is a standing wave, and the excitation sound wave intensity is maximum.
In order to meet the demands of modern communication technologies for higher communication transmission rates, denser connection densities, and larger amounts of communication data, SAW filters that are widely used in radio frequency front ends are required to have greater bandwidths. The conventional SAW resonator structure is fixed after fabrication, which results in a SAW resonator based filter that has a relatively fixed operating band and bandwidth, which is highly detrimental to the use of such filters in modern communication systems. To address this problem, scholars have proposed solutions that exploit the acousto-electric effect (acoustoelectric effect, AE effect) to achieve SAW resonator center frequency tuning. This approach generally affects the characteristics of SAW propagation along the surface of the piezoelectric material by changing the conductivity of the surface.
The SAW excited by the IDT is accompanied by an alternating electric field of the same period as the SAW when propagating along the surface of the piezoelectric layer, which means that the charge distribution of the SAW propagation path also has periodicity. If the conductivity of the surface of the piezoelectric material can be dynamically adjusted by the external conditions, the electric field along with the SAW propagation can have different losses on the surface of the piezoelectric material, and finally the purpose of changing the SAW propagation speed, namely the acousto-electric effect caused by the change of the conductivity of the surface of the piezoelectric layer, is achieved. It is possible to obtain, according to the perturbation theory, a reduction in SAW velocity due to the acoustoelectric effect as:
k in the formula 2 Is the electromechanical coupling coefficient of the piezoelectric layer, v 0 For SAW velocity, σ, unaffected by changes in surface conductivity of the piezoelectric layer S Epsilon is the conductivity of the piezoelectric layer surface S Dielectric constant, ε, of the surface of the piezoelectric layer 0 Is the vacuum dielectric constant.
The document [ Kohji Hohkawa etal, 268 Jpn. J.appl. Phys.477104] has proposed two-dimensional electron gas (2 DEG) coupling with SAW using AlGaN/GaN heterojunction interfaces to achieve tuning of SAW resonators. The SAW resonator structure of this scheme is shown in fig. 1, and by applying a certain dc voltage to the interdigital electrode pair, continuous adjustment of the concentration of 2DEG at the AlGaN/GaN interface can be achieved, so as to achieve continuous adjustment of the conductivity of the semiconductor surface, and finally achieve continuous adjustment of the center frequency of the SAW resonator, as shown in fig. 1.
The SAW resonator based on AlGaN/GaN heterostructures described above has the following drawbacks:
(1) The 2DEG concentration at the AlGaN/GaN heterojunction interface is mainly affected by the thickness of the AlGaN barrier layer 202, and typically the 2DEG concentration is positively correlated to the AlGaN barrier layer 202 thickness; literature [.F.Medjdaub, et al, appl. Phys. Lett.2011, vol98,223502]It is reported that the heterojunction structure generally requires the AlGaN barrier layer 202 to be not less than 10nm to effectively induce 2DEG, whereas up to only 10 a can be achieved by increasing the thickness of the AlGaN barrier layer 202 13 /cm 2 A 2DEG concentration of the order of magnitude. The upper concentration limit of the 2DEG on the one hand determines the maximum range over which the conductivity of the structure can be adjusted. On the other hand, thicker AlGaN barrier layer 202 may result in a device requiring higher DC voltage to achieve adjustment of its 2DEG concentration, due toThis can introduce certain limitations to the design of tunable SAW resonators based on AlGaN/GaN heterojunction structures;
(2) In SAW devices based on AlGaN/GaN heterojunction structures, the pair of interdigital electrodes directly contacts the AlGaN barrier layer 202 to form schottky contact, and when a direct current voltage is applied, a large leakage current is generated, which results in a problem that the loss of the device is large and the device is prone to generate heat. In the literature [ N.Shigekawa, et al EEE Electron Device Letters, vol.28, no.2, pp.90-92, feb.2007 ]]In the case of SAW resonators based on AlGaN/GaN heterostructures, the 2DEG concentration is 9.02X10 12 /cm 2 When the AlGaN barrier layer is 21nm thick, the depletion voltage of the 2DEG is-2.5V, and the direct current variation range is-10V-0V. The larger depletion voltage easily causes excessive leakage current to cause large heating value and quickens the ageing and the damage of the device.
Disclosure of Invention
The invention aims to provide a reconfigurable SAW resonator structure and a preparation method thereof, so as to avoid the problems of thicker dielectric layer, low carrier concentration, high DC bias voltage and large leakage current caused by introducing the thicker dielectric layer on a piezoelectric material.
The reconfigurable SAW resonator structure comprises a substrate and an epsilon-phase gallium oxide piezoelectric film arranged on the substrate;
the upper end part of the epsilon-phase gallium oxide piezoelectric film, which is far away from the substrate, is provided with a conductive layer by injecting negative ions; disposing a dielectric layer over the conductive layer; providing a pair of interdigital electrodes on the dielectric layer; one interdigital electrode is respectively connected with a direct-current bias voltage and an RF signal, and the other interdigital electrode is grounded.
The negative ions are fluoride ions.
The preparation method of the reconfigurable SAW resonator structure comprises the following steps:
s1, growing an epsilon-phase gallium oxide piezoelectric film on a substrate;
s2, injecting negative ions into the surface of the epsilon-phase gallium oxide piezoelectric film to form a conductive layer at the upper end part of the epsilon-phase gallium oxide piezoelectric film;
s3, growing a dielectric layer on the surface of the conductive layer;
s4, utilizing a mask to manufacture a pair of interdigital electrodes on the surface of the dielectric layer;
s5, removing a mask for manufacturing the interdigital electrode.
And in the step S2, negative ions are injected into the surface of the epsilon-phase gallium oxide piezoelectric film by utilizing the plasma of the fluorine-based gas, wherein the negative ions are fluorine ions.
The fluorine-based gas is CF 4 。
The step S2 is accomplished by using an RIE/ICP-RIE system.
And (3) after the epsilon-phase gallium oxide piezoelectric film grows in the step (S1), an acid washing process is further carried out.
The pickling process comprises the following steps: soaking in FN solution, and washing with DIW; then soaking in SPM solution, and then flushing with DIW;
the FN solution is HF, HNO 3 Mixed solution=1:1;
the SPM solution was 98% H 2 SO 4 :30％ H 2 O 2 Diw=1:1:4 mixed solution;
the DIW is deionized water.
The soaking time in FN solution was 1 minute.
The soaking time in the SPM solution was 5 minutes.
The reconfigurable SAW resonator structure and the preparation method thereof have the advantages that the concentration of the two-dimensional electron gas induced on the surface of the epsilon-phase gallium oxide piezoelectric film after the negative ions are injected can reach as high as 10 14 ～10 15 /cm 2 The magnitude of the carrier concentration increase is not limited by thickness. On the one hand, on the basis of unlimited thickness, the SAW resonator is more flexible and simpler than the existing solutions in design and manufacture. On the other hand, the high-concentration two-dimensional electron gas is more sensitive to the change of the direct-current bias voltage, and can be in a working state only by a lower voltage. After the insulating dielectric layer is introduced, no leakage current exists, and the problem of large heating value is avoided.
Drawings
Fig. 1 is a schematic cross-sectional view of a SAW resonator of the prior art.
Fig. 2 is a schematic cross-sectional view of a reconfigurable SAW resonator structure in accordance with the present invention.
Fig. 3 is a graph of dc bias voltage versus carrier concentration for a reconfigurable SAW resonator structure in accordance with the present invention.
Fig. 4 is a thermodynamic diagram of the electric field change caused by RF small signals for a reconfigurable SAW resonator structure of the present invention under a-0.5V dc bias.
Fig. 5 is a thermodynamic diagram of the electric field change caused by RF small signals for a reconfigurable SAW resonator structure of the present invention under a 0.5V dc bias.
Fig. 6 is a graph of dielectric layer thickness versus two-dimensional electron gas depletion voltage for a reconfigurable SAW resonator structure in accordance with the present invention.
FIG. 7 is a schematic flow chart of the preparation method of the present invention.
FIG. 8 is a second schematic flow chart of the preparation method of the present invention.
FIG. 9 is a third schematic flow chart of the preparation method of the present invention.
FIG. 10 is a schematic diagram showing a flow chart of the production method of the present invention.
FIG. 11 is a fifth flow chart of the preparation method of the present invention.
Fig. 12 is a perspective view of a reconfigurable SAW resonator structure in accordance with the present invention.
Reference numerals:
a substrate 101, an epsilon-phase gallium oxide piezoelectric film 102, a conductive layer 103, a dielectric layer 104, interdigital electrodes 105 and a mask 106;
gallium nitride layer 201, alGaN barrier layer 202.
Detailed Description
As shown in fig. 2, a reconfigurable SAW resonator structure of the present invention includes a substrate 101, and an epsilon-phase gallium oxide piezoelectric film 102 disposed on the substrate 101. The upper end part of the epsilon-phase gallium oxide piezoelectric film 102, which is far away from the substrate 101, is provided with a conductive layer 103 by injecting negative ions. A dielectric layer 104 is provided on the conductive layer 103. A pair of interdigital electrodes 105 is provided on the dielectric layer 104. One of the interdigital electrodes 105 is connected to a dc bias voltage and an RF signal, respectively, and the other interdigital electrode 105 is grounded. The 2DEG concentration can be adjusted by applying different dc bias voltages to the interdigital electrodes 105 to achieve a reconstruction of the electrical characteristics of the SAW resonator. In the present invention, the carriers are electrons.
The technical characteristics of the reconfigurable SAW resonator structure in the invention are as follows:
because the 2DEG is formed by surface induction, compared with the heterojunction structure in the prior art, the process of constructing the heterojunction can be omitted, and the production process is correspondingly simplified; and the concentration of the 2DEG is not limited by the thickness of the material, so that the size design of the SAW resonator is more flexible and is more suitable for on-chip operation. The concentration of 2DEG can reach 10 by the surface negative ion implantation 14 -10 15 /cm 2 The magnitude is one to two orders of magnitude higher than the upper limit of the heterojunction structure, so that the regulating range of the SAW resonator is correspondingly larger, and the regulating efficiency is higher. Dielectric layer 104 is relatively insulating and the SAW resonator is substantially free of leakage current during operation, thereby avoiding the problem of high heating.
The fluoride ion is selected as the material to be implanted, but is only a preferable scheme, and the technology of the invention can be realized without limiting the specific material. Under the technical conception disclosed in the invention, a person skilled in the art can reasonably select Nb ions, sn ions, si ions, ge ions and the like for implantation, so that the 2DEG with the corresponding high concentration is realized.
In this embodiment, the preferred embodiment is described, and the negative ion is a fluoride ion. The fluoride ion source is preferably CF 4 The gas mainly consists of a large radius of carbon atoms, and is not easy to be injected into the epsilon-phase gallium oxide piezoelectric film 102.
The working principle of the reconfigurable SAW resonator structure disclosed by the invention is as follows:
the 2DEG concentration of the conductive layer 103 is changed by applying a dc bias, so as to adjust the conductivity of the conductive layer 103, change the SAW velocity propagating along the surface of the epsilon-phase gallium oxide piezoelectric film 102, and finally achieve the purpose of adjusting the center frequency. As shown in fig. 2, the dc bias is used to adjust the 2DEG concentration and the RF signal is used to excite the SAW. When the negative dc bias applied is not large enough, the high concentration of 2DEG will shield the RF signal, and the entire resonator will be off, no longer exciting the SAW.
In the tunable SAW resonator structure of the present invention, the 2DEG concentration is determined by the process parameters during the fluorine-based plasma treatment, and the initial state is not affected by the thickness of the dielectric layer 104. There is no particular requirement for the thickness of the dielectric layer 104 in the design and fabrication of such tunable SAW resonators, reducing device structural design limitations. The thickness of the dielectric layer 104 only affects the range of values of the dc bias and the 2DEG depletion voltage.
Within a certain range, the applied negative pressure repels electrons downwards, and the concentration of the 2DEG is reduced; conversely, an applied positive pressure concentrates the electron attraction to the surface and the 2DEG concentration increases. As shown in fig. 3, the results of 2DEG simulation at different dc biases for a dielectric layer 104 thickness of 10 nm. The 2DEG concentration affects the wave velocity of the SAW, i.e., affects the center frequency of the SAW resonator. The strength of the RF signal affects the strength of the SAW excitation. In practical work, a person skilled in the art can reasonably select corresponding direct current bias voltages to adjust according to different center frequency demands and RF signal intensities of application occasions, so as to avoid shielding the RF signals by the high-concentration 2DEG. As shown by simulation results, the concentration of the 2DEG can be more than 10 under the premise that the DC bias is not more than 1V 5 /cm 2 SAW resonators have high tuning efficiency and tuning range.
The simulation will be presented below using an RF signal as an example of a small signal. The small signal Δv=0.1v, and the dc bias applied to the interdigital electrode 105 is specifically selected to be-0.5V and 0.5V. The piezoelectric effect strength caused by the RF signals under different DC biases can be represented by simulating the electric field variation of the epsilon-phase gallium oxide piezoelectric film 102 caused by the small signals under different DC biases. As shown in fig. 4, when the dc bias is-0.5V, the small signal induced electric field variation can pass through the corresponding conductive layer 103 of the 2DEG, i.e., an effective SAW excitation can be created, as part of the 2DEG is depleted. As shown in fig. 5, when the dc bias is 0.5V, electrons of the conductive layer 103 are more concentrated on the surface, thereby shielding the change of the electric field caused by the small signal, and the SAW cannot be excited at this time.
The effect of the thickness of the dielectric layer 104 on the dc bias voltage regulation 2DEG is shown below. When different dielectric layer 104 thicknesses are used, the dc bias voltage required to deplete the 2DEG will also be different. Because the dielectric layer 104 is insulating, the structure can avoid the problem of leakage current while the thickness of the dielectric layer 104 is less than 10 nm. As shown in fig. 6, when the thickness of the dielectric layer 104 is less than 5nm, only a dc bias voltage of about-0.14V is required to deplete the 2DEG. Therefore, the tunable SAW resonator adopting the structure can carry out larger-range adjustment on the 2DEG concentration only by small direct current voltage, thereby realizing higher adjustment efficiency and lower energy loss.
The preparation method of the reconfigurable SAW resonator structure comprises the following specific steps:
an epsilon-phase gallium oxide piezoelectric film 102 with a certain thickness is grown on a substrate 101 by adopting an epitaxial growth method, so as to obtain a sample structure shown in fig. 7. The substrate 101 may be sapphire, siC, si, or the like. Methods of epitaxial growth may include MOCVD, MBE, PLD, or the like.
Carrying out inorganic acid washing on the sample: after 1 minute of immersion in FN solution, rinse with dediw. After subsequent 5 minutes of immersion in SPM solution, a rinse with deionized water was used. And removing the surface defect layer and improving the injection effect of fluorine element. The FN solution is a mixed solution of HF and HNO3=1:1; the SPM solution is a mixed solution of 98% H2SO4:30% h2o2:diw=1:1:4; the DIW is deionized water. The proportion of all solutions in the examples is the volume ratio.
Fluorine-based plasma treatment was performed on the epsilon-phase gallium oxide piezoelectric film 102 using an RIE/ICP-RIE system, and a high concentration of 2DEG was formed on the upper end portion of the epsilon-phase gallium oxide piezoelectric film 102 to obtain a corresponding conductive layer 103, as shown in fig. 8. The selected fluorine-based gas is CF 4 Preferably, the radius of the carbon atoms is larger, so that the epsilon-phase gallium oxide piezoelectric film 102 is not easy to inject.
Growing a dielectric layer 104 on the conductive layer 103 by atomic layer deposition, magnetron sputtering, or the like, e.gFig. 9 shows the same. The dielectric layer 104 may be selected from SiO 2 、Al 2 O 3 Etc.
A mask 106 is introduced over the dielectric layer 104 and patterned to expose the areas where the interdigitated electrodes 105 are to be formed, as shown in fig. 10.
A pair of interdigital electrodes 105 are formed by depositing a metal by electron beam vapor deposition or the like, and after development and stripping, a mask 106 and an unnecessary metal outside the interdigital electrodes 105 are removed, as shown in fig. 11 and 12.
And finally, configuring proper direct current bias and RF signals to obtain the reconfigurable SAW resonator structure shown in figure 2.
It will be apparent to those skilled in the art from this disclosure that various other changes and modifications can be made which are within the scope of the invention as defined in the appended claims.
Claims (10)
1. A reconfigurable SAW resonator structure comprising a substrate (101), and an epsilon-phase gallium oxide piezoelectric film (102) disposed on the substrate (101);
it is characterized in that the method comprises the steps of,
the upper end part of the epsilon-phase gallium oxide piezoelectric film (102) far away from the substrate (101) is provided with a conductive layer (103) by injecting negative ions; -providing a dielectric layer (104) on the conductive layer (103); a pair of interdigital electrodes (105) disposed on the dielectric layer (104); one of the interdigital electrodes (105) is connected with a DC bias voltage and an RF signal, and the other interdigital electrode (105) is grounded.
2. A reconfigurable SAW resonator structure according to claim 1, wherein the negative ions are fluoride ions.
3. A method of making a reconfigurable SAW resonator structure comprising the steps of:
s1, growing an epsilon-phase gallium oxide piezoelectric film (102) on a substrate (101);
s2, injecting negative ions into the surface of the epsilon-phase gallium oxide piezoelectric film (102) to enable the upper end part of the epsilon-phase gallium oxide piezoelectric film (102) to form a conductive layer (103);
s3, growing a dielectric layer (104) on the surface of the conductive layer (103);
s4, manufacturing a pair of interdigital electrodes (105) on the surface of the dielectric layer (104) by using a mask (106);
s5, removing a mask for manufacturing the interdigital electrode (105).
4. The method according to claim 3, wherein in the step S2, negative ions, which are fluorine ions, are injected into the surface of the epsilon-phase gallium oxide piezoelectric film (102) by using a plasma of fluorine-based gas.
5. The method according to claim 4, wherein the fluorine-based gas is CF 4 。
6. The method of claim 3, wherein step S2 is performed using an RIE/ICP-RIE system.
7. The method according to claim 3, wherein the step S1 is further performed with an acid washing step after the epsilon-phase gallium oxide piezoelectric film (102) is grown.
8. The method according to claim 7, wherein the pickling process comprises: soaking in FN solution, and washing with DIW; then soaking in SPM solution, and then flushing with DIW;
the FN solution is HF, HNO 3 Mixed solution=1:1;
the SPM solution was 98% H 2 SO 4 :30％H 2 O 2 Diw=1:1:4 mixed solution;
the DIW is deionized water.
9. The method of claim 8, wherein the soaking time in the FN solution is 1 minute.
10. The method of claim 8, wherein the soaking time in the SPM solution is 5 minutes.
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| CN202310658269.8A Pending CN116760382A (en) | 2023-06-05 | 2023-06-05 | Reconfigurable SAW resonator structure and preparation method |
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| CN (1) | CN116760382A (en) |
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