Patent ID: 12199587

Throughout the drawings and the detailed description, unless otherwise described, the same drawing reference numerals will be understood to refer to the same elements, features, and structures. The relative size and depiction of these elements may be exaggerated for clarity, illustration, and convenience.

DETAILED DESCRIPTION

The following description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. Accordingly, various changes, modifications, and equivalents of the methods, apparatuses, and/or systems described herein will be suggested to those of ordinary skill in the art. Also, descriptions of well-known functions and constructions may be omitted for increased clarity and conciseness.

FIG.1is a reference diagram illustrating a structure of a surface acoustic wave (SAW) device100according to an embodiment of the present invention.

Referring toFIG.1, the SAW device100includes a substrate110, an intermediate layer120, a piezoelectric layer130, and an inter-digital transducer (IDT) electrode140.

The substrate110may be made of any one of a silicon (Si) material, a sapphire material, and a diamond material. A surface orientation of the substrate110is not particularly limited, and may be any of, for example, <111>, <100>, and <110>, or these surface orientations may exist in a mixed manner. The thickness of the substrate110may be 5 [μm] or more, or twice or more of the wavelength, in consideration of vibration of SAW.

An upper portion of the substrate110is deformed by a predetermined thickness by an ion implant so that an ion trap layer is formed, and the intermediate layer120is formed on an upper surface of the ion trap layer110-1. The ion trap layer110-1may refer to a substrate in which the substrate110made of crystalline silicon (Si) material, sapphire material, or diamond material is amorphized.

FIG.2is a reference diagram illustrating an ion implantation state for forming the ion trap layer110-1on the upper portion of the substrate110.

When an ion implant is performed with the same energy, the smaller the size of the ions, the deeper the ions can travel into the substrate110, but since the size of the ions are small, a large amount of ions should be implanted. Conversely, when the size of ions is large, relatively large energy is required to implant the ions, but due to the large ion size, the same ion implantation function can be achieved with fewer ions as compared to using the ions of small size.

FIG.3is a graph showing the degree of amorphization of the substrate110according to the depth when various types of ions are implanted onto the substrate110.

Ion implantation is a process by which various ions are implanted into the substrate110by being accelerated with an electric field so that the ions can have a large energy enough to penetrate the surface of the substrate110. Examples of types of ions to be implanted may include argon ions, silicon ions, neon ions, or nitrogen ions.

It is confirmed that the most similar results of ion implantation (e.g., constant thickness or the like) are achieved when an energy of 350 keV is applied for argon ions, an energy of 270 KeV is applied for silicon ions, an energy of 170 KeV is applied for neon ions, and an energy of 150 KeV is applied for nitrogen ions. The amount of energy to be applied may increase as the size of ions increases, and the amount of energy to be applied may decrease as the size of ions decreases. At this time, in terms of the depth of the ion trap layer110-1formed in the substrate110, nitrogen ions, which are light elements, are most advantages due to the sharpest ion gradient, but the dose density tends to be lowered near the surface.

Due to the formation of the ion trap layer110-1on the substrate110made of the silicon material, sapphire material, or diamond material, the silicon material, sapphire material, or diamond material is amorphized, and the amorphized substrate110may function as a trap layer to prevent leakage of SAW energy toward the substrate. In order to function as a trap layer for preventing energy leakage, the ion trap layer110-1formed on the substrate110may have a thickness of from 0.4 μm to 0.6 μm.

FIG.4is a graph showing the magnitude of the Bode quality factor according to formation of ion implantation compared to the conventional one.

Referring toFIG.4, it can be seen that, as compared to a case A in which an existing amorphous trap layer is separately formed between the substrate110and the intermediate layer120, a case B in which an ion implantation is formed in the substrate110provide an equal or higher Bode quality value of the SAW device. Therefore, it can be confirmed that the ion implantation process is effective in terms of difficulty in manufacturing process, manufacturing time, or cost since less time and lower difficulty in manufacturing are required as compared to the process of separately forming the amorphous trap layer while the SAW device having the substrate110formed by the ion implantation process still has the equivalent quality factor to that of the existing amorphous trap layer.

The intermediate layer120is a layer formed on the upper surface of the substrate110. The intermediate layer120has the function of controlling the crystalline characteristics of the piezoelectric layer130positioned thereon, and may be made of SiO2material, AlN material, or the like.

The thickness of the intermediate layer120may be appropriately selected according to the type, size, purpose of use, and the like of the underlying substrate110, and may be preferably in a range between 5 and 500 nm. The reason is that if the intermediate layer120is thinner than the lower limit of the above range, the function of controlling the crystalline characteristics of the piezoelectric layer130tends to be insufficient, and if the intermediate layer120is thicker than the upper limit of the above range, the electromechanical coupling coefficient k2 becomes small, which makes it difficult to excite the SAW. In addition, the thickness of the intermediate layer120may be obtained by observing a cut surface of the SAW device with a film thickness measurement device, for example, a scanning electron microscope (SEM) or the like. The intermediate layer120has an insulation level such that its resistivity is preferably not less than about 104 Ω·cm. This is because if the resistivity of the intermediate layer120is lower than 104 Ω·cm, the conductivity becomes high, which may cause power loss.

The piezoelectric layer130is a layer formed on an upper surface of the intermediate layer120. The piezoelectric layer130may be made of LiNbO3(LN), LiTaO3(LT), or the like, and may be single crystalline. In addition, the thickness of the piezoelectric layer130is not particularly limited, and may be appropriately selected according to application of the SAW device100.

Also, in order to improve the piezoelectric properties of the SAW device100, the piezoelectric layer130may be made of LiNbO3. The piezoelectric layer130may be formed by a bonding process. The bonding methods include atomic diffusion bonding (ADB) and surface activation bonding (SAB) methods, and a method of forming the thickness of the piezoelectric layer includes a grinding method and an ion cut method.

The IDT electrode140is an electrode formed on the upper surface of the piezoelectric layer130to generate SAWs. The IDT electrode140may be a single comb-shaped electrode or a double comb-shaped electrode. The material for forming the IDT electrode140is not particularly limited, but the IDT electrode140may be selected from Al, Al—Cu, Al—Si—Cu, and the like in consideration of processability and cost.

The thickness of the IDT electrode140may be set to any desired range so long as the IDT electrode140can develop the function of exciting SAWs, but it is preferably in the range of about 10 to 500 nm. This is because if the thickness of the IDT electrode140is less than 10 nm, the resistivity becomes high, resulting in an increased loss, and if the thickness of the IDT electrode140exceeds 500 nm, the mass effect of the electrodes upon producing SAW reflection is noticeable and the desired SAW characteristics would be impeded.

In addition, the IDT electrode140may be disposed such that it is buried in the surface of the piezoelectric layer130. More specifically, by way of example, recessed grooves are formed in the surface of the piezoelectric layer130, and a conductive material, such as Al, which forms the IDT electrode140, is completely or partially buried in the recessed grooves. By burying the whole or part of the IDT electrode140in the underlying layer, the height of the IDT electrode140can be made almost equal to that of the surface in which the IDT electrode140is to be formed. Consequently, it is possible to reduce the effect caused by the thickness of the IDT electrode140upon SAW reflection.

FIG.5is a flowchart illustrating an embodiment for describing a method of manufacturing a SAW device according to the present invention, andFIG.6is a reference diagram illustrating a stacked structure according to a manufacturing process of the SAW device ofFIG.5.

First, a substrate is formed (operation S200). Various methods may be used to form the substrate, and specifically, the methods may include a chemical vapor deposition (CVD) method, a microwave plasma CVD method, a physical vapor deposition (PVD) method, a sputtering method, an ion planting method, a plasma jet method, a flame method, a hot filament method, and so on.

After operation S200, an ion implantation process is performed on the upper portion of the substrate to form an ion trap layer in which the upper portion of the substrate is deformed by a predetermined thickness (operation S202). The ion trap layer corresponds to a layer in which the substrate110made of a silicon (Si) material, sapphire material, or diamond material is amorphized.

Examples of types of ions used for ion implantation may include argon ions, silicon ions, neon ions, or nitrogen ions. For example, an energy of 350 keV may be applied for argon ions, an energy of 270 KeV may be applied for silicon ions, an energy of 170 KeV may be applied for neon ions, and an energy of 150 KeV may be applied for nitrogen ions. The substrate made of the silicon material, sapphire material, or diamond material is amorphized, so that the leakage of the SAW energy through the substrate can be prevented. In order to function as a trap layer for preventing energy leakage, the ion trap layer formed on the substrate may have a thickness of from 0.4 μm to 0.6 μm.

In the case of a process of forming an ion trap layer by ion implantation, the energy (keV) applied and the amount of implanted ions (ion/sqcm) may be different for each ion type as shown in Table 1 below.

TABLE 1EnergyDoseSpecie(keV)(ion/sqcm)CostProcessNitrogen1506.0 E15Low costHigh risk (Largemodeling difference)Neon1702.4 E15Intermediate costEffectiveSilicon2701.6 E15High costLow riskArgon3501.2 E15Low costHigh risk

Referring to Table 1, in the case of nitrogen ions with small particle size, relatively small energy (e.g., 150 keV) is applied, and as the particle size of the ions increases, higher energy is applied. Thus, in the case of argon ions, an energy of 350 keV is applied. On the other hand, reviewing the amount of ions to be injected from Table 1, in the case of nitrogen ions with small particle size, a large amount of ions (e.g., 6.0 E15 ion/sqcm) is implanted, and as the particle size of ions increases, a smaller amount of ions is implanted. Thus, in the case of argon ions, 6.0 E15 ion/sqcm is implanted.

Accordingly, reviewing the efficiency, the nitrogen ions are advantageous in terms of cost since the applied energy is small, but there is a relatively high possibility that variations in the effect as an ion trap layer may occur. On the other hand, in the case of silicon ions, since the applied energy is large, the silicon ions are disadvantageous compared to nitrogen ions or neon ions in terms of cost, but they are advantageous in that there is little possibility that variations in the effect as an ion trap layer occur.

Meanwhile, in the ion implantation process according to the present invention, the ion trap layer may be formed by one ion implantation process, but the ion trap layer may be formed by at least two ion implantation processes.

Table 2 shows the comparison of ion implantation efficiency of each ion according to two ion implantation processes.

TABLE 21st Energy1st Dose2nd Energy2nd DoseSpecie(keV)(ion/sqcm)(keV)(ion/sqcm)Nitrogen1502.5 E15501.0 E15Neon1701.5 E15854.5 E14Silicon2708.5 E141354.0 E14Argon3507.0 E141753.0 E14

Referring to Table 2, in the case of nitrogen ions, an ion amount of 2.5 E15 ion/sqcm is implanted into the substrate110with an energy of 150 keV in a primary implantation process and an ion amount of 1.0 E15 ion/sqcm is implanted into the substrate110with an energy of 50 keV in a secondary implantation process. In the case where ions are implanted twice, the total amount of ions to be implanted is 2.5 E15+1.0 E15 ion/sqcm, which is smaller than the ion amount of 6.0 E15 ion/sqcm of the single ion implantation process in Table 1, and the equivalent ion trap layer can be formed even with such a small amount of ions. Therefore, when ions are implanted by performing the ion implantation process two or more times, it is advantageous in terms of energy consumption rate.

Meanwhile, in the above description, the ion implantation process is described as being performed two or more times by varying the energy or the amount of ions, but the ion implantation process may be performed two or more times with the same energy or the same amount of ions. In other words, the ion trap layer may be formed through at least two or more ion implantation processes by varying at least one of factors including energy, the amount of ions, and time.

Similarly to the case of nitrogen ions, an ion trap layer may be formed by performing two or more ion implantation processes for neon ions, silicon ions, and argon ions. In particular, in the case of silicon ions, the total amount of ions implanted by the two implantation processes is 8.5 E14+4.0 E14 ion/sqcm, whereas in Table 1, the amount of ions implanted by the single implantation process is 1.6 E15 ion/sqcm. Thus, the two ion implantation processes are quite efficient in terms of energy consumption. Therefore, it is preferable to form the ion trap layer by the implantation of silicon ions by performing the ion implantation process two or more time, rather than only once.

After operation S202, an intermediate layer is formed on an upper surface of the ion trap layer (operation S204). The intermediate layer has the function of controlling the crystalline characteristics of the piezoelectric layer130positioned thereon, and may be made of SiO2material, AlN material, or the like. The thickness of the intermediate layer may be appropriately selected according to the type, size, purpose of use, and the like of the underlying substrate110, and may be in a range between 5 and 500 nm. The reason is that if the intermediate layer is thinner than the lower limit of the above range, the function of controlling the crystalline characteristics of the piezoelectric layer tends to be insufficient, and if the intermediate layer is thicker than the upper limit of the above range, the electromechanical coupling coefficient becomes small, which makes it difficult to excite the SAW. The intermediate layer may be formed by various vapor deposition methods, such as a CVD method, a PVD method, a sputtering method, an ion plating method, and the like.

After operation S204, a piezoelectric layer is formed on an upper surface of the intermediate layer (operation S206). The piezoelectric layer may be made of LiNbO3(LN), LiTaO3(LT), or the like, and may be single crystalline. In addition, the thickness of the piezoelectric layer is not particularly limited, and may be appropriately selected according to application of the SAW device. The piezoelectric layer may be formed by a bonding process. The bonding methods include ADB and SAB methods, and a method of forming the thickness of the piezoelectric layer includes a grinding method and an ion cut method.

After operation S206, an IDT electrode for generating a SAW is formed on the upper surface of the piezoelectric layer (operation S208).

The IDT electrode may be a single comb-shaped electrode or a double comb-shaped electrode. The IDT electrode may be made of Al, Al—Cu, Al—Si—Cu, or the like. The thickness of the IDT electrode may be set to any desired range so long as the IDT electrode140can develop the function of exciting SAWs, but it is preferably in the range of about 10 to 500 nm. Recessed grooves are formed in the surface of the piezoelectric layer130, and a conductive material, such as Al, which forms the IDT electrode, is completely or partially buried in the recessed grooves.

According to the present invention, an intermediate layer is formed on an upper surface of a substrate, a piezoelectric layer is formed on an upper surface of the intermediate layer, an IDT electrode is formed on an upper surface of the piezoelectric layer, and an ion trap layer is formed by an ion implantation in an upper portion of the substrate so that the loss of SAW energy in the direction of the substrate is prevented by the ion trap layer. Accordingly, by suppressing the loss of the SAW energy in the direction of the substrate, it is possible to prevent reduction of quality factor.

In addition, the ion trap layer is formed on the substrate by performing the ion implantation process two or more times, it is possible to minimize excessive energy consumption for the formation of the ion trap layer. In addition, it is possible to prevent the energy of the existing SAW from dissipating through the substrate.

A number of examples have been described above. Nevertheless, it will be understood that various modifications may be made. For example, suitable results may be achieved if the described techniques are performed in a different order and/or if components in a described system, architecture, device, or circuit are combined in a different manner and/or replaced or supplemented by other components or their equivalents. Accordingly, other implementations are within the scope of the following claims.