High-frequency sound surface wave device and preparation method that a kind of AlN film is the intermediate layer
Technical field
The present invention relates to the SAW device technical field, high-frequency sound surface wave device and preparation method that particularly a kind of AlN film is the intermediate layer.
Background technology
In recent years, mobile communication rapid development makes radio communication frequency bands become a limited and valuable natural resources.For GSM, the frequency band that is lower than 1GHz has been taken (first generation digital system); The frequency of second generation digital system is from 900MHz to 1.9GHz; In third generation digital system, global roaming trip trip frequency range is 1.8~2.2GHz, and global position system (GPS) frequency is 1.575GHz; The applying frequency scope of the new satellite communication of Low Earth Orbit (LEO) is 1.6GHz~2.5GHz; Therefore, the applying frequency of present GSM is increasingly high, is badly in need of surface acoustic wave (SAW) filter of high frequency; And, move logical moving communicator and all require the try one's best miniaturization and have bigger power bearing ability of surface acoustic wave SAW filter.
For conventional SAW material (for example, quartzy, LiNbO
3, LiTaO
3, ZnO etc.), the velocity of sound lower (all being lower than 4000m/s) is made the SAW device of 2.5GHz with it; Its IDT finger beam d must be less than 0.4 μ m, and the finger beam d of 5GHz correspondence approaches the limit of present semi-conductor industry level less than 0.2 μ m; Cause severed finger serious, rate of finished products is too low.And d is more little, and resistance is just big more, and power bearing ability is more little, has seriously restricted the further raising of SAW device frequency; At present, hanker after both at home and abroad reaching the effect that improves frequency through improving velocity of sound V.Because diamond has the highest modulus of elasticity (E=1200Gpa) and the low (ρ=3.519/cm of density of material in all material
3), the highest longitudinal wave velocity characteristics such as (18000m/s) is so diamond is the optimal material of this method.And diamond itself does not have piezoelectric property, can't carry out acoustic-electric conversion, still adopt diamond to combine with piezoelectric the multilayer film system.The performance of SAW is determined by piezoelectric membrane and diamond substrate jointly.The velocity of sound of ZnO is 2600m/s, differs especially big with the adamantine velocity of sound, causes velocity of sound frequency dispersion easily, and phase velocity alters a great deal with the frequency difference.
2008; People such as TaiWan, China Sean Wu combine the AlN film of a-axle preferrel orientation first with diamond; The AlN film that obtains the a-axle preferrel orientation through finite element simulation has higher sound degree than the AlN film of c axle preferrel orientation, sound scooter 10474m/s, and piezoelectric modulus K
2Reach 2.31%.People such as the Taiwan Ruyen Ro AlN film that in many pieces of articles, proposes the a-axle preferrel orientation again is more suitable for the application of high frequency SAW device afterwards.This provides theoretical foundation for the application of AlN film in high frequency SAW device of a-axle preferrel orientation, and the relevant report through the experiment confirm this point is not arranged so far as yet.
Therefore, press at present and develop a kind of multilayer film substrate that can improve the SAW device frequency, and electromechanical coupling factor is high, can bear high-power through minimizing velocity of sound frequency dispersion.
Summary of the invention
The objective of the invention is to above-mentioned technical Analysis and existing problems; High-frequency sound surface wave device and preparation method that a kind of AlN film is provided is the intermediate layer; This high-frequency sound surface wave device is a ZnO/a-axle preferrel orientation AlN/ diamond multilayer membrane structure; This structure SAW device frequency is high, and can bear high-powerly, and satisfies the requirement of high-frequency and high-power mobile communication; This preparation method's device therefor is simple, process conditions are convenient and easy, help applying on a large scale, is of great practical significance.
Technical scheme of the present invention:
A kind of AlN film is the high-frequency sound surface wave device in intermediate layer, as the intermediate layer between CVD diamond substrate and the c-axle preferrel orientation ZnO film, forms IDT/ZnO/a-axle preferrel orientation AlN/ diamond multilayer membrane structure with the AlN film of a-axle preferrel orientation.Promptly superpose successively and constitute by AlN film, c-axle preferrel orientation ZnO film and the interdigital transducer IDT of Nano diamond substrate, a-axle preferrel orientation.
The crystal grain dimension of described intermediate layer a-axle preferrel orientation AlN film is that 60-80nm, thickness are 0.2-0.3 μ m; The crystal grain dimension of the ZnO film of described upper strata c-axle preferrel orientation is 60-90nm, thickness 0.7-0.8 μ m.
The preparation method that a kind of said AlN film is the high-frequency sound surface wave device in intermediate layer, step is following:
1) adopt the CVD method to prepare the Nano diamond substrate;
2) with the Al target as target, adopt radio-frequency magnetron sputter method to prepare a-axle preferrel orientation AlN film at the Nano diamond substrate surface;
3) with the ZnO ceramic target as target, adopt radio-frequency magnetron sputter method to prepare the ZnO film of c-axle preferrel orientation at a-axle preferrel orientation AlN film surface;
4) adopt the ZnO film surface preparation interdigital transducer IDT of electron-beam vapor deposition method at the c-axle preferrel orientation.
The technological parameter that described employing CVD method prepares the Nano diamond bottom is: in argon gas, hydrogen and methane blended gas, carry out chemical vapor deposition; The percent by volume of argon gas, hydrogen and methane is 75%: 20%: 5%; Mixed gas flow is 500sccm; Microwave power is that 4500W, pressure are 75Pa in the deposit cavity, and underlayer temperature is 750 ℃, and sedimentation time is 2 hours.
The radio frequency magnetron technological parameter that described Nano diamond substrate surface prepares a-axle preferrel orientation AlN film is: in nitrogen and argon gas mist, react, the volume ratio of nitrogen and argon gas is 7: 13, and the purity of nitrogen and argon gas is 99.999%; Underlayer temperature is 300 ℃, and target-substrate distance 8cm, sputtering power are 110W; Operating air pressure 1.2Pa, sputtering time are 2 hours, close argon gas then; Continue to feed nitrogen and slowly lower the temperature, the time that feeds nitrogen is 30 minutes.
The said radio frequency magnetron technological parameter for preparing c-axle preferrel orientation ZnO at the AlN of a-axle preferrel orientation film surface is: in oxygen and argon gas mist, react; The volume ratio of oxygen and argon gas is 4: 8, and the purity of oxygen and argon gas is 99.999%, 400 ℃ of underlayer temperatures; Target-substrate distance 8cm; Radio-frequency power 70W, operating air pressure 1.2Pa, sputtering time 2 hours.
The method of said ZnO film surface preparation interdigital transducer IDT at the c-axle preferrel orientation: adopt the aluminium Al film of the method for electron beam evaporation at the about 100nm of ZnO film surface deposition one layer thickness of c-axle preferrel orientation; Roughness is less than 4nm; Using the photoetching method to process finger beam then is the equivalent interdigital of 1.6 μ m, and interdigital logarithm is 50 pairs
Advantage of the present invention and technique effect are:
1) between the ZnO of c-axle preferrel orientation and diamond, add-layer a-axle as thin as a wafer remove the AlN film thought according to qualifications, constitutes multi-layer film structure and can show very little speed frequency dispersion, and this is a biggest advantage of the present invention.In principle, after diamond reaches certain thickness, multilayer film phase velocity, electromechanical coupling factor (K
2) all closely related with piezoelectric membrane, the piezoelectric membrane thickness that the two peak value is corresponding different, if multilayer film phase velocity (V) difference is little, the multilayer film phase velocity one more smooth with the piezoelectric membrane varied in thickness in a big way, can give raising electromechanical coupling factor (K
2) a bigger selection space, help reaching simultaneously high frequency and Gao Gao electromechanical coupling factor (K
2);
2) adamantine phase velocity (V) is the highest in all material; Can reach 18000m/s; The phase velocity 11354m/s of the AlN thin-film material of a-axle preferrel orientation itself; Relatively approaching adamantine phase velocity, and between ZnO and diamond phase velocity, so " the AlN/ diamond of ZnO/a-axle preferrel orientation " multi-layer film structure velocity of sound V should be higher than " ZnO/ diamond ", " LiNbO
3/ diamond " structures such as " c-axle preferrel orientation AlN/ diamonds ", thus when interdigital transducer finger beam d is identical, can reach higher frequency;
3) ZnO suppresses electric material, and diamond is a non-piezoelectric material, and the AlN film of a-axle preferrel orientation also has piezoelectric property, so the AlN film of a-axle preferrel orientation is of value to the raising electromechanical coupling factor as ZnO and adamantine intermediate layer;
4) the AlN film of diamond, a-axle preferrel orientation, ZnO thermal conductivity are all very high, have good cooling mechanism; Therefore thermal coefficient of expansion is all very little, has good frequency-temperature characteristic (TCD is approximately zero), and when device bears high-power temperature when raising, centre frequency raises with temperature and drifts about very for a short time, and this is very big advantage, especially as far as narrow band filter;
5) the AlN film of ZnO, a-axle preferrel orientation, diamond three compare, and it is very little that lattice constant differs, and it is also less that mass density, modulus of elasticity differ, and at the AlN film of the firm a-axle preferrel orientation of diamond substrate preparation combination, the interlayer defective is less.
So select " ZnO/a-axle preferrel orientation AlN film/diamond " as SAW device multi-layer film structure, can prepare high frequency, high-power, high electromechanical coupling factor (K
2), low loss and the centre frequency propagated be with the temperature very little SAW device of drift that raises.
Description of drawings
Fig. 1 is this multilayer film SAW device structural representation.
Fig. 2 is AFM (AFM) surface topography map of a-axle preferrel orientation AlN film.
The displayed map of Fig. 3 for when the surperficial radio frequency sputtering of diamond substrate deposits a axle preferrel orientation AlN film, using X-ray diffractometer (XRD) to characterize.Show among the figure:, near 2 θ=33.2 ° peak value is arranged when film a-axle preferrel orientation is grown.
Specific embodiments
In order to make those skilled in the art person understand the present invention program better, the present invention is done further detailed description below in conjunction with accompanying drawing and execution mode.
Embodiment:
The first step, with the nano-diamond membrane substrate of CVD method preparation:
The technological parameter that said employing CVD method prepares the Nano diamond bottom is: in argon gas, hydrogen and methane blended gas, carry out chemical vapor deposition; The percent by volume of argon gas, hydrogen and methane is 75%: 20%: 5%; Mixed gas flow is 500sccm; Microwave power is that 4500W, pressure are 75Pa in the deposit cavity, and underlayer temperature is 750 ℃, and sedimentation time is 2 hours.
Second step, in the high vacuum sputtering chamber, as target, carry out the sputter of high vacuum magnetic control with hydrogen termination and bright finished CVD diamond film surface with the Al target above-mentioned, deposition forms one deck a-axle preferrel orientation AlN film, thickness 0.30 μ m:
In nitrogen and argon gas mist, react, the volume ratio of nitrogen and argon gas is 7: 13, and the purity of nitrogen and argon gas is 99.999%; Underlayer temperature is 300 ℃, and target-substrate distance 8cm, sputtering power are 110W; Operating air pressure 1.2Pa, sputtering time are 2 hours, close argon gas then; Continue to feed nitrogen and slowly lower the temperature, the time that feeds nitrogen is 30 minutes.
Accompanying drawing 2 has shown through the in-situ annealing atomic force surface topography map afterwards with the nitrogen ending.
The displayed map that accompanying drawing 3 has used X-ray diffractometer (XRD) to characterize when having shown on diamond substrate surface radio frequency sputtering deposition a-axle preferrel orientation AlN film when film a-axle preferrel orientation is grown, has peak value near 2 θ=33.2 °.
The 3rd the step, in the high vacuum sputtering chamber, as target, carry out the sputter of high vacuum magnetic control with a-axle preferrel orientation AlN film surface with the ZnO ceramic target above-mentioned, prepare the ZnO film of high c-axle preferrel orientation, thickness 0.7 μ m:
In oxygen and argon gas mist, react, the volume ratio of oxygen and argon gas is 4: 8, and the purity of oxygen and argon gas is 99.999%, 400 ℃ of underlayer temperatures, target-substrate distance 8cm, radio-frequency power 70W, operating air pressure 1.2Pa, sputtering time 2 hours.
The 4th step, at the ZnO film surface preparation interdigital transducer IDT of c-axle preferrel orientation:
Adopt the aluminium Al film of electron-beam vapor deposition method at the about 100nm of ZnO film surface deposition one layer thickness of c-axle preferrel orientation, roughness is less than 4nm, and using the photoetching method to process finger beam then is the equivalent interdigital of 1.6 μ m, and interdigital logarithm is 50 pairs.
Fig. 1 is this multilayer film SAW device structural representation.
The invention provides a kind of high-performance ZnO/a-axle preferrel orientation AlN/ diamond multilayer membrane structure surface acoustic wave substrate; Its frequency is high; And can bear high-powerly, can satisfy the requirement of high-frequency and/or high-power mobile communication, in addition; The present invention also provides a kind of method of preparation this high-performance ZnO/a-axle preferrel orientation AlN/ diamond multilayer membrane structure SAW device; This preparation method's device therefor is simple, process conditions are convenient and easy, help applying on a large scale, is of great practical significance.
The above only is a preferred implementation of the present invention; Should be pointed out that for those skilled in the art, under the prerequisite that does not break away from the principle of the invention; Can also make some improvement and retouching, these improvement and retouching also should be regarded as protection scope of the present invention.