A matching layer for an ultrawide bandwidth acousto-optic deflector and a method of manufacture

Abstract

The application provides a matching layer of an ultrawideband acoustooptic deflector and a preparation method thereof, which is used for acoustic impedance matching between a piezoelectric crystal and an acoustooptic crystal of the acoustooptic deflector. The matching layer is arranged between the piezoelectric crystal and the acoustooptic crystal. The matching layer comprises a first bottom electrode of tin material plated at a bottom end surface of the piezoelectric crystal, a second bottom electrode of aluminum material plated at a top end surface of the acoustooptic crystal, and a third bonding layer of indium material between the first bottom electrode and the second bottom electrode. A top electrode of silver material is arranged at a top end surface of the piezoelectric crystal. The application can prepare an acoustooptic deflector component with ultrahigh bandwidth.

Description

Technical Field

[0001] This invention relates to the field of acousto-optic deflector technology, and in particular to a matching layer for an ultra-wide bandwidth acousto-optic deflector and its fabrication method. Background Technology

[0002] Piezoelectric transducers are a crucial component of acousto-optic deflectors, influencing their bandwidth. Because of the acoustic impedance mismatch between the piezoelectric crystal and the acousto-optic crystal, several matching layers need to be deposited between them to achieve acoustic impedance matching. A piezoelectric transducer mainly consists of a top electrode, a piezoelectric crystal, a third bonding layer, and a bottom electrode. The third bonding layer and the bottom electrode form the matching layers between the piezoelectric crystal and the acousto-optic crystal.

[0003] In device design, the bandwidth of the acousto-optic deflector is affected by the design of the piezoelectric transducer. In the selection of matching layer materials for the piezoelectric transducer, it is difficult to find materials that are exactly equal to the calculated theoretical acoustic impedance value, and the number of matching layers, structure, and thickness also affect the bandwidth of the acousto-optic deflector.

[0004] Existing coating methods (PVD, magnetron sputtering, etc.) are difficult to achieve the deposition of thick metal films. They can generally only be deposited to a thickness of less than 2 micrometers. When the thickness is too thick, problems such as film peeling, cracking, and poor surface finish will occur, which will make it difficult to prepare the transducer matching layer.

[0005] In order to obtain a relatively wide 3dB bandwidth for the acousto-optic deflector within the operating frequency range of the device, the proposed invention focuses on the selection of matching layer material, number of matching layers, structure and thickness design of the matching layer of the piezoelectric transducer to achieve the goal of ultra-wide 3dB bandwidth for the acousto-optic deflector, and has developed a corresponding device fabrication method. Summary of the Invention

[0006] This invention proposes a matching layer for an ultra-wide bandwidth acousto-optic deflector and a method for its fabrication, which can be used to fabricate acousto-optic deflector components with ultra-high bandwidth.

[0007] The present invention adopts the following technical solution.

[0008] A matching layer for an ultra-wide bandwidth acousto-optic deflector is provided for acoustic impedance matching between the piezoelectric crystal and the acousto-optic crystal of the acousto-optic deflector. The matching layer is disposed between the piezoelectric crystal and the acousto-optic crystal. The matching layer includes a first bottom electrode made of tin plated on the bottom end face of the piezoelectric crystal, a second bottom electrode made of aluminum plated on the top end face of the acousto-optic crystal, and a third bonding layer made of indium between the first bottom electrode and the second bottom electrode. A top electrode made of silver is provided on the top end face of the piezoelectric crystal.

[0009] The top electrode, piezoelectric crystal, third bonding layer, and bottom electrode are the constituent elements of the piezoelectric transducer in the acousto-optic deflector. The piezoelectric transducer is driven by a power supply. The formula for calculating the matching loss of the piezoelectric transducer, which reflects how much of the electrical power output by the power supply can be absorbed by the piezoelectric transducer, is as follows:

[0010]

[0011] Where Ps is the matching power provided by the piezoelectric transducer drive power supply, and Pt is the power absorbed by the piezoelectric transducer; the formula for calculating the internal conversion loss, which reflects how much of the power absorbed by the piezoelectric transducer can be converted into ultrasonic power absorbed by the acousto-optic crystal, is as follows:

[0012]

[0013] Wherein, Pm is the ultrasonic power absorbed by the acousto-optic crystal;

[0014] The total transducer loss of a piezoelectric transducer is defined as the sum of the matching loss and the internal conversion loss, as shown in the formula:

[0015]

[0016] The matching layer is a double-layer matching layer; the piezoelectric crystal has an acoustic impedance of Zo, and the acousto-optic crystal has an acoustic impedance of Zao. Let Zp1 be the theoretical acoustic impedance of the matching layer near the piezoelectric crystal, and its calculation formula is:

[0017] Let Zp2 be the theoretical acoustic impedance of the matching layer near the acousto-optic crystal, and its calculation formula is:

[0018]

[0019] The silver layer thickness of the top electrode is 0.56 μm; the piezoelectric crystal is made of lithium niobate material and has an acoustic impedance of 33.9 × 10⁻⁶ μm. 6 kg / (m 2 The acousto-optic crystal is 37 μm thick and made of quartz crystal, with an acoustic impedance of 15.2 × 10⁻⁶. 6 kg / (m 2 ·s).

[0020] The theoretical acoustic impedance of the matching layer near the piezoelectric crystal is 24 × 10⁻⁶. 6 kg / (m 2 The theoretical acoustic impedance of the matching layer near the acousto-optic crystal is 15.2 × 10⁻⁶ Ω·s. 6 kg / (m 2 The acoustic impedance of the first bottom electrode is slightly greater than the calculated theoretical acoustic impedance, which is 24.2 × 10⁻⁶. 6 kg / (m 2The second bottom electrode has a thickness of 12 μm and an acoustic impedance slightly greater than the calculated theoretical acoustic impedance, which is 17.3 × 10⁻⁶. 6 kg / (m 2 The thickness of the third bonding layer is 220 μm; the thickness of the third bonding layer is 6.6 μm.

[0021] The center frequency of the acousto-optic deflector is 80MHz, and its 3dB bandwidth reaches 59MHz.

[0022] A method for preparing a matching layer for an ultrawide bandwidth acousto-optic deflector, used to prepare the matching layer for the ultrawide bandwidth acousto-optic deflector described above, characterized in that: the preparation method includes the following steps;

[0023] Step S1: Press-weld Al sheet onto the quartz crystal;

[0024] Step S2: Bond the Sn sheet to the piezoelectric crystal;

[0025] Step S3: Weld the quartz crystal and the piezoelectric crystal to form a composite crystal;

[0026] Step S4: Thinning the combined crystal;

[0027] Step S5: After the thinned composite crystal is subjected to sound absorption treatment and cleaned, the required surface electrode is deposited by vacuum coating; the acousto-optic crystal is now complete.

[0028] Step S1 includes the following steps;

[0029] Step A1: Prepare an Al sheet with a thickness of 219 μm;

[0030] Step A2: A 0.5 μm Al coating layer is simultaneously deposited on the quartz crystal and Al sheet using vacuum coating. In this step, the coating thickness is adjusted according to the customized Al sheet thickness to achieve a total Al sheet thickness of 220 μm after double-sided coating. Immediately after coating, heating and pressure are applied to weld the Al sheet and the quartz crystal to form quartz crystal component A.

[0031] Step S2 includes the following steps;

[0032] Step B1: Prepare a Sn wafer with a thickness of 11 μm;

[0033] Step B2: Use a thick piezoelectric crystal to reduce cracking in subsequent processes. Vacuum deposit 0.5um Sn on the piezoelectric crystal and Sn sheet with a thickness of not less than 2mm. Adjust the coating thickness according to the thickness of the customized Sn sheet to achieve a total thickness of 12um for the Sn sheet after double-sided coating. Immediately after coating, heat and pressure are applied to weld the Sn sheet and piezoelectric crystal to form piezoelectric crystal component B.

[0034] Step B3 includes the following steps;

[0035] Step C1: Prepare a 6µm In wafer;

[0036] Step C2: Polish the Al sheet of component A and the Sn sheet of component B to a mirror-grade roughness Ra0.1.

[0037] Step C3: Simultaneously deposit a 0.3µm thick indium layer on the polished Al sheet of component A and the Sn sheet of component B under vacuum; adjust the coating thickness according to the customized In sheet thickness to achieve a total thickness of 6.6µm for the In sheet and the two indium coatings.

[0038] Step C4: Immediately after plating, heat and pressurize to connect component A and component B;

[0039] Step S4 specifically involves thinning the welded acousto-optic crystal to 37µm through rough grinding, high polishing, and fine polishing processes.

[0040] After completing step S5, the acousto-optic crystal electrode is impedance matched and can then be used to fabricate the designed ultrawide bandwidth acousto-optic deflector.

[0041] In the above scheme, Al represents the element aluminum, and Al sheet is an aluminum sheet; Sn represents the element tin, and Sn sheet is a tin sheet; In represents the element indium, and In sheet is an indium sheet.

[0042] This invention optimizes the selection of matching layer material, the number of matching layers, the structure, and the thickness of the matching layer in piezoelectric transducers, enabling the achievement of an ultra-wide 3dB bandwidth in acousto-optic deflectors.

[0043] This invention employs a thick matching layer design, while existing coating methods (PVD, magnetron sputtering, etc.) have difficulty in achieving thick metal film deposition, generally only able to deposit to below 2 micrometers. When the deposition is thick, problems such as film peeling, cracking, and poor surface finish will occur. In order to achieve such a thick matching layer and reduce it to the required thickness, this invention designs a special matching layer preparation process that can prepare a thick metal coating layer structure. Attached Figure Description

[0044] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0045] Appendix Figure 1 This is a schematic diagram of the structure of the present invention;

[0046] Appendix Figure 2 This is a schematic diagram illustrating the simulation performance of the acousto-optic deflector described in this invention;

[0047] In the figure: 1-top electrode; 2-piezoelectric crystal; 3-first bottom electrode; 4-third bonding layer; 5-second bottom electrode; 6-acousto-optic crystal. Detailed Implementation

[0048] As shown in the figure, a matching layer for an ultra-wide bandwidth acousto-optic deflector is used for acoustic impedance matching between the piezoelectric crystal 2 and the acousto-optic crystal 6 of the acousto-optic deflector. The matching layer is disposed between the piezoelectric crystal and the acousto-optic crystal. The matching layer includes a first bottom electrode 3 made of tin plated on the bottom end face of the piezoelectric crystal, a second bottom electrode 6 made of aluminum plated on the top end face of the acousto-optic crystal, and a third bonding layer 4 made of indium between the first bottom electrode and the second bottom electrode. A top electrode 1 made of silver is provided on the top end face of the piezoelectric crystal.

[0049] The top electrode, piezoelectric crystal, third bonding layer, and bottom electrode are the constituent elements of the piezoelectric transducer in the acousto-optic deflector. The piezoelectric transducer is driven by a power supply. The formula for calculating the matching loss of the piezoelectric transducer, which reflects how much of the electrical power output by the power supply can be absorbed by the piezoelectric transducer, is as follows:

[0050]

[0051] Where Ps is the matching power provided by the piezoelectric transducer drive power supply, and Pt is the power absorbed by the piezoelectric transducer; the formula for calculating the internal conversion loss, which reflects how much of the power absorbed by the piezoelectric transducer can be converted into ultrasonic power absorbed by the acousto-optic crystal, is as follows:

[0052]

[0053] Wherein, Pm is the ultrasonic power absorbed by the acousto-optic crystal;

[0054] The total transducer loss of a piezoelectric transducer is defined as the sum of the matching loss and the internal conversion loss, as shown in the formula:

[0055]

[0056] The matching layer is a double-layer matching layer; the piezoelectric crystal has an acoustic impedance of Zo, and the acousto-optic crystal has an acoustic impedance of Zao. Let Zp1 be the theoretical acoustic impedance of the matching layer near the piezoelectric crystal, and its calculation formula is:

[0057] Let Zp2 be the theoretical acoustic impedance of the matching layer near the acousto-optic crystal, and its calculation formula is:

[0058]

[0059] The silver layer thickness of the top electrode is 0.56 μm; the piezoelectric crystal is made of lithium niobate material and has an acoustic impedance of 33.9 × 10⁻⁶ μm. 6 kg / (m2 The acousto-optic crystal is 37 μm thick and made of quartz crystal, with an acoustic impedance of 15.2 × 10⁻⁶. 6 kg / (m 2 ·s).

[0060] The theoretical acoustic impedance of the matching layer near the piezoelectric crystal is 24 × 10⁻⁶. 6 kg / (m 2 The theoretical acoustic impedance of the matching layer near the acousto-optic crystal is 15.2 × 10⁻⁶ Ω·s. 6 kg / (m 2 The acoustic impedance of the first bottom electrode is slightly greater than the calculated theoretical acoustic impedance, which is 24.2 × 10⁻⁶. 6 kg / (m 2 The second bottom electrode has a thickness of 12 μm and an acoustic impedance slightly greater than the calculated theoretical acoustic impedance, which is 17.3 × 10⁻⁶. 6 kg / (m 2 The thickness of the third bonding layer is 220 μm; the thickness of the third bonding layer is 6.6 μm.

[0061] The center frequency of the acousto-optic deflector is 80MHz, and its 3dB bandwidth reaches 59MHz.

[0062] A method for preparing a matching layer for an ultrawide bandwidth acousto-optic deflector, used to prepare the matching layer for the ultrawide bandwidth acousto-optic deflector described above, characterized in that: the preparation method includes the following steps;

[0063] Step S1: Press-weld Al sheet onto the quartz crystal;

[0064] Step S2: Bond the Sn sheet to the piezoelectric crystal;

[0065] Step S3: Weld the quartz crystal and the piezoelectric crystal to form a composite crystal;

[0066] Step S4: Thinning the combined crystal;

[0067] Step S5: After the thinned composite crystal is subjected to sound absorption treatment and cleaned, the required surface electrode is deposited by vacuum coating; the acousto-optic crystal is now complete.

[0068] Step S1 includes the following steps;

[0069] Step A1: Prepare an Al sheet with a thickness of 219 μm;

[0070] Step A2: A 0.5 μm Al coating layer is simultaneously deposited on the quartz crystal and Al sheet using vacuum coating. In this step, the coating thickness is adjusted according to the customized Al sheet thickness to achieve a total Al sheet thickness of 220 μm after double-sided coating. Immediately after coating, heating and pressure are applied to weld the Al sheet and the quartz crystal to form quartz crystal component A.

[0071] Step S2 includes the following steps;

[0072] Step B1: Prepare a Sn sheet with a thickness of 11 μm;

[0073] Step B2: Use a thick piezoelectric crystal to reduce cracking in subsequent processes. Vacuum deposit 0.5um Sn on the piezoelectric crystal and Sn sheet with a thickness of not less than 2mm. Adjust the coating thickness according to the thickness of the customized Sn sheet to achieve a total thickness of 12um for the Sn sheet after double-sided coating. Immediately after coating, heat and pressure are applied to weld the Sn sheet and piezoelectric crystal to form piezoelectric crystal component B.

[0074] Step B3 includes the following steps;

[0075] Step C1: Prepare a 6µm In wafer;

[0076] Step C2: Polish the Al sheet of component A and the Sn sheet of component B to a mirror-grade roughness Ra0.1.

[0077] Step C3: Simultaneously deposit a 0.3µm thick indium layer on the polished Al sheet of component A and the Sn sheet of component B under vacuum; adjust the coating thickness according to the customized In sheet thickness to achieve a total thickness of 6.6µm for the In sheet and the two indium coatings.

[0078] Step C4: Immediately after plating, heat and pressurize to connect component A and component B;

[0079] Step S4 specifically involves thinning the welded acousto-optic crystal to 37µm through rough grinding, high polishing, and fine polishing processes.

[0080] After completing step S5, the acousto-optic crystal electrode is impedance matched and can then be used to fabricate the designed ultrawide bandwidth acousto-optic deflector.

Claims

1. A matching layer for an ultra-wide bandwidth acousto-optic deflector, used for acoustic impedance matching between the piezoelectric crystal and the acousto-optic crystal of the acousto-optic deflector, characterized in that: The matching layer is disposed between the piezoelectric crystal and the acousto-optic crystal. The matching layer includes a first bottom electrode made of tin plated on the bottom end face of the piezoelectric crystal, a second bottom electrode made of aluminum plated on the top end face of the acousto-optic crystal, and a third bonding layer made of indium between the first bottom electrode and the second bottom electrode. A top electrode made of silver is disposed on the top end face of the piezoelectric crystal. A method for fabricating a matching layer for an ultrawide bandwidth acousto-optic deflector, the method comprising the following steps; Step S1: Weld an aluminum sheet onto the top surface of the acousto-optic crystal; Step S2: Press solder sheet onto the bottom surface of the piezoelectric crystal; Step S3: Weld the acousto-optic crystal and the piezoelectric crystal to form a composite crystal; Step S4: Thinning the combined crystal; Step S5: After the thinned composite crystal is subjected to sound absorption treatment and cleaned, the required top electrode is deposited using vacuum coating; the composite crystal is now complete. In step S1, an aluminum sheet is first prepared, and an aluminum coating layer is simultaneously deposited on the acousto-optic crystal and the aluminum sheet using a vacuum coating method. In this step, the coating thickness is adjusted according to the thickness of the aluminum sheet, and the aluminum sheet is coated on both sides. After coating, the aluminum sheet is heated and pressurized immediately to achieve the welding of the aluminum sheet and the acousto-optic crystal, forming the acousto-optic crystal component A. In step S2, a tin sheet is first prepared. A thick piezoelectric crystal is used to reduce cracking in subsequent processes. Tin is simultaneously deposited on the piezoelectric crystal and the tin sheet with a thickness of not less than 2 mm using a vacuum plating method. The plating thickness is adjusted according to the thickness of the tin sheet to achieve double-sided plating. After plating, heating and pressure are applied immediately to weld the tin sheet and the piezoelectric crystal to form piezoelectric crystal component B. Then, indium sheets are prepared first. The polished aluminum sheet of component A and the tin sheet of component B are simultaneously plated with indium layers under vacuum. The coating thickness is adjusted according to the thickness of the indium sheet to achieve the required total thickness of the indium sheet and the two indium coatings. Immediately after plating, heating and pressurization are applied to connect component A and component B.

2. The matching layer of an ultra-wide bandwidth acousto-optic deflector according to claim 1, characterized in that: The top electrode, piezoelectric crystal, third bonding layer, and bottom electrode are the constituent elements of the piezoelectric transducer in the acousto-optic deflector. The piezoelectric transducer is driven by a power supply. The formula for calculating the matching loss of the piezoelectric transducer, which reflects how much of the electrical power output by the power supply can be absorbed by the piezoelectric transducer, is as follows: Formula 1; Where Ps is the matching power provided by the piezoelectric transducer drive power supply, and Pt is the power absorbed by the piezoelectric transducer. The formula for calculating the internal conversion loss, which reflects how much of the power absorbed by the piezoelectric transducer can be converted into ultrasonic power absorbed by the acousto-optic crystal, is as follows: Formula 2; Where Pm is the ultrasonic power absorbed by the acousto-optic crystal; The total transducer loss of a piezoelectric transducer is defined as the sum of the matching loss and the internal conversion loss, as shown in the formula: Formula 3; The acoustic impedance of a piezoelectric crystal is Zo, and the acoustic impedance of an acousto-optic crystal is Zao. Let Zp1 be the theoretical acoustic impedance of the matching layer near the piezoelectric crystal, and its calculation formula is: Formula 5; Let Zp2 be the theoretical acoustic impedance of the matching layer near the acousto-optic crystal, and its calculation formula is: Formula Six.

3. The matching layer of an ultra-wide bandwidth acousto-optic deflector according to claim 2, characterized in that: The silver layer thickness of the top electrode is 0.56 μm; the piezoelectric crystal is made of lithium niobate material and has an acoustic impedance of 33.9 × 10⁻⁶ μm. 6 kg / (m 2 The acousto-optic crystal is 37 μm thick and made of quartz crystal, with an acoustic impedance of 15.2 × 10⁻⁶. 6 kg / (m 2 ·s).

4. The matching layer of an ultra-wide bandwidth acousto-optic deflector according to claim 3, characterized in that: The theoretical acoustic impedance of the matching layer near the piezoelectric crystal is 24 × 10⁻⁶. 6 kg / (m 2 The theoretical acoustic impedance of the matching layer near the acousto-optic crystal is 15.2 × 10⁻⁶ Ω·s. 6 kg / (m 2 The acoustic impedance of the first bottom electrode is slightly greater than the calculated theoretical acoustic impedance, which is 24.2 × 10⁻⁶. 6 kg / (m 2 The second bottom electrode has a thickness of 12 μm and an acoustic impedance slightly greater than the calculated theoretical acoustic impedance, which is 17.3 × 10⁻⁶. 6 kg / (m 2 The thickness of the third bonding layer is 220 μm; the thickness of the third bonding layer is 6.6 μm.

5. The matching layer of an ultra-wide bandwidth acousto-optic deflector according to claim 4, characterized in that: The center frequency of the acousto-optic deflector is 80MHz, and its 3dB bandwidth reaches 59MHz.

6. A method for preparing a matching layer for an ultrawide bandwidth acousto-optic deflector, used to prepare the matching layer for the ultrawide bandwidth acousto-optic deflector as described in claim 4, characterized in that: The preparation method includes the following steps; Step S1: Weld aluminum sheet onto quartz crystal; Step S2: Press solder sheet onto the piezoelectric crystal; Step S3: Weld the quartz crystal and the piezoelectric crystal to form a composite crystal; Step S4: Thinning the combined crystal; Step S5: After the thinned composite crystal is subjected to sound absorption treatment and cleaned, the required top electrode is deposited using vacuum coating; the composite crystal is now complete.

7. The method for preparing the matching layer of the ultra-wide bandwidth acousto-optic deflector according to claim 6, characterized in that: Step S1 includes the following steps; Step A1: Prepare an aluminum sheet with a thickness of 219 μm; Step A2: A 0.5µm aluminum coating layer is simultaneously deposited on the quartz crystal and aluminum sheet using vacuum coating. In this step, the coating thickness is adjusted according to the customized aluminum sheet thickness to achieve a total aluminum sheet thickness of 220µm after double-sided coating. Immediately after coating, heating and pressure are applied to weld the aluminum sheet and quartz crystal to form quartz crystal component A. Step S2 includes the following steps; Step B1: Prepare a tin sheet with a thickness of 11 μm; Step B2: Use a thick piezoelectric crystal to reduce cracking in subsequent processes. Vacuum plate 0.5um of tin on the piezoelectric crystal and tin sheet with a thickness of not less than 2mm. Adjust the plating thickness according to the thickness of the customized tin sheet to achieve a total thickness of 12um for the tin sheet after double-sided plating. Immediately after plating, heat and pressure are applied to weld the tin sheet and piezoelectric crystal to form piezoelectric crystal component B. Step S3 includes the following steps; Step C1: Prepare a 6µm indium wafer; Step C2: Polish the aluminum sheet of component A and the tin sheet of component B to a mirror-grade roughness Ra0.

1. Step C3: Simultaneously deposit a 0.3µm thick indium layer on the polished aluminum sheet of component A and the tin sheet of component B under vacuum; adjust the coating thickness according to the customized indium sheet thickness to achieve a total thickness of 6.6µm for the indium sheet and the two indium coatings. Step C4: Immediately after plating, heat and pressurize to connect component A and component B; Step S4 specifically involves thinning the welded acousto-optic crystal to 37µm through rough grinding, high polishing, and fine polishing processes. After completing step S5, the combined crystal-deposited top electrode, after impedance matching, can be used to fabricate the designed ultrawide bandwidth acousto-optic deflector.

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