阅读说明：本技术 体声波滤波器 (Bulk acoustic wave filter ) 是由 李源祥 于 2018-06-11 设计创作，主要内容包括：提供了一种用于使预设频率范围内的电信号通过的体声波(BAW)滤波器(130)。BAW滤波器(130)包括：金刚石基板(114)；钝化层(111),其形成在所述金刚石基板(114)上；第一金属层(110),其形成在所述钝化层(111)上；压电层(104’),其形成在所述第一金属层(110)上；第二金属层(116),其形成在压电层(104’)上；金属焊盘(120),其形成在所述第一金属层(110)上。所述金属焊盘(120)、所述第一金属层(110)、所述压电层(104’)和所述第二金属层(116)形成电路径,该电路径允许预设频率范围内的电信号通过。(A Bulk Acoustic Wave (BAW) filter (130) for passing electrical signals in a predetermined frequency range is provided. The BAW filter (130) comprises: a diamond substrate (114); a passivation layer (111) formed on the diamond substrate (114); a first metal layer (110) formed on the passivation layer (111); a piezoelectric layer (104') formed on the first metal layer (110); a second metal layer (116) formed on the piezoelectric layer (104'); a metal pad (120) formed on the first metal layer (110). The metal pad (120), the first metal layer (110), the piezoelectric layer (104'), and the second metal layer (116) form an electrical path that allows electrical signals within a preset frequency range to pass through.)

1. A Bulk Acoustic Wave (BAW) filter, the BAW filter comprising:

a diamond substrate.

2. The bulk acoustic wave filter of claim 1, further comprising:

a passivation layer formed on the diamond substrate;

a first metal layer formed on the passivation layer;

a piezoelectric layer formed on the first metal layer;

a second metal layer formed on the piezoelectric layer; and

a metal pad formed on the first metal layer,

wherein the metal pad, the first metal layer, the piezoelectric layer, and the second metal layer form an electrical path that allows electrical signals in a frequency range to pass through.

3. The bulk acoustic wave filter of claim 2, further comprising:

a seed layer disposed between the diamond substrate and the passivation layer, the seed layer being formed of diamond powder and used to grow the diamond substrate thereon.

4. The bulk acoustic wave filter of claim 1, wherein the passivation layer is formed of a dielectric material.

5. The bulk acoustic wave filter of claim 1, wherein the piezoelectric layer is formed of a material having a piezoelectric effect.

6. The bulk acoustic wave filter of claim 1, wherein the piezoelectric layer comprises at least one of GaN, AlN, and ZnO.

7. The bulk acoustic wave filter of claim 2, wherein each of the first metal layer, the second metal layer, and the metal pad is formed of a conductive metal.

8. The bulk acoustic wave filter according to claim 1, wherein the diamond substrate has at least one of a single crystal structure and a polycrystalline structure.

9. A method of manufacturing a bulk acoustic wave filter, the method comprising:

forming a piezoelectric layer;

forming a first metal layer on a first surface of the piezoelectric layer;

forming a first passivation layer on the first metal layer;

forming a diamond substrate on the first passivation layer;

forming a second metal layer on a second surface of the piezoelectric layer;

removing a portion of the piezoelectric layer to expose a portion of the first metal layer; and

a metal pad is formed on the exposed portion of the first metal layer.

10. The method of claim 9, wherein the step of forming a diamond substrate comprises:

forming a seed layer on the first passivation layer; and

and growing the diamond substrate on the seed crystal layer.

11. The method of claim 9, wherein the seed layer is formed from diamond powder.

12. The method of claim 9, wherein the step of forming a piezoelectric layer comprises:

forming the piezoelectric layer on a substrate;

forming a second passivation layer on the piezoelectric layer; and is

Forming a dummy wafer on the second passivation layer; and

and removing the substrate.

13. The method of claim 12, further comprising:

after the step of forming a diamond substrate, removing the dummy wafer and the second passivation layer.

14. The method of claim 12, wherein the dummy wafer is formed of silicon.

15. The method of claim 9, wherein the piezoelectric layer comprises at least one of GaN, AlN, and ZnO.

16. The method of claim 9, wherein each of the first metal layer, the second metal layer, and the metal pad is formed from a conductive metal.

17. The method of claim 9, wherein the first passivation layer comprises at least one of polysilicon and silicon nitride.

18. A non-transitory computer readable medium carrying one or more pattern data sequences for fabricating a bulk acoustic wave filter, wherein execution of the one or more pattern data sequences by one or more processors causes the one or more processors to perform the steps of:

forming a piezoelectric layer;

forming a first metal layer on a first surface of the piezoelectric layer;

forming a first passivation layer on the first metal layer;

forming a diamond substrate on the first passivation layer;

forming a second metal layer on a second surface of the piezoelectric layer;

removing a portion of the piezoelectric layer to expose a portion of the first metal layer; and

a metal pad is formed on the exposed portion of the first metal layer.

19. The non-transitory computer readable medium of claim 18, wherein the one or more pattern data sequences are executed by one or more processors such that the one or more processors perform the step of forming the diamond substrate by performing the steps of:

forming a seed layer on the first passivation layer; and

and growing the diamond substrate on the seed crystal layer.

20. The non-transitory computer-readable medium of claim 18, wherein execution of the one or more sequences of pattern data by one or more processors causes the one or more processors to perform the step of forming a piezoelectric layer by performing the steps of:

forming the piezoelectric layer on a substrate;

forming a second passivation layer on the piezoelectric layer;

forming a dummy wafer on the second passivation layer;

and removing the substrate.

Technical Field

The present invention relates to a Radio Frequency (RF) signal filter, and more particularly, to a Bulk Acoustic Wave (BAW) filter and a method of manufacturing the same.

Background

BAW filters that can remove signals in unwanted frequency ranges are commonly used in various wireless frequency communication devices, such as mobile phones. As the size and weight of mobile devices are reduced while various functions are added to the mobile devices, modern mobile devices require BAW filters having a factor of reducing the shape and a factor of enhancing the quality. Accordingly, Bulk Acoustic Wave (BAW) filter technology has been rapidly developing over the past decade to meet the needs of communication devices.

Generally, BAW filters have BAW resonators fabricated on silicon, gallium arsenide or glass substrates. During operation, BAW resonators may generate thermal energy that needs to be discharged through the substrate to the outside of the BAW filter. If the thermal energy is not properly discharged, it may affect the resonant frequency, overall performance, and durability of the BAW filter. The thermal characteristics of conventional substrates may not be suitable for efficiently removing thermal energy from BAW resonators, such that BAW filters may not be useful in devices that generate large amounts of thermal energy.

Fig. 10A and 10B illustrate a process of forming a conventional BAW filter 1000. As shown, a piezoelectric layer 1004 is deposited on the silicon wafer 1002, and a first metal layer 1006 is deposited on the piezoelectric layer 1004. Since silicon has a relatively low acoustic wave velocity, it is necessary to remove a portion 1010 of the silicon wafer below the operating area of the piezoelectric layer 1004 so that the piezoelectric layer 1004 is in direct contact with the first metal layer 1006 and the second metal layer 1008 (i.e., the BAW filter has a free-standing configuration). This process adds to the manufacturing process. Furthermore, conventional fabrication processes use sputtering techniques to deposit a piezoelectric layer 1004 on a silicon wafer 1002. However, when using sputtering techniques, it is difficult to control the thickness and uniformity of the piezoelectric layer 1004 if the thickness of the piezoelectric layer 1004 is less than 100 angstroms.

Thus, there is a need for a BAW filter having a mechanism for releasing thermal energy from the BAW filter in an efficient manner while reducing the manufacturing cost of the BAW filter without compromising the quality of the piezoelectric layer.

Disclosure of Invention

In an embodiment, a Bulk Acoustic Wave (BAW) filter includes: a diamond substrate; a passivation layer formed on the diamond substrate; a first metal layer formed on the passivation layer; a piezoelectric layer formed on the first metal layer; a second metal layer formed on the piezoelectric layer; and a metal pad formed on the first metal layer. The metal pad, the first metal layer, the piezoelectric layer, and the second metal layer form an electrical path that allows electrical signals within a preset frequency range to pass through.

In an embodiment, a method of manufacturing a bulk acoustic wave filter includes: forming a piezoelectric layer; forming a first metal layer on a first surface of the piezoelectric layer; forming a first passivation layer on the first metal layer; forming a diamond substrate on the first passivation layer; forming a second metal layer on a second surface of the piezoelectric layer; removing a portion of the piezoelectric layer to expose a portion of the first metal layer; and forming a metal pad on the exposed portion of the first metal layer.

Drawings

Reference will now be made to embodiments of the invention, examples of which may be illustrated in the accompanying drawings. The drawings are illustrative and not restrictive. While the invention is generally described in the context of these embodiments, it will be understood that it is not intended to limit the scope of the invention to these particular embodiments.

Fig. 1-7 illustrate an exemplary process for forming a BAW filter according to an embodiment of the disclosure.

Fig. 8 is a top view of the BAW filter of fig. 7, in accordance with an embodiment of the present disclosure.

Fig. 9 shows a flow diagram of an exemplary process for manufacturing a BAW filter according to an embodiment of the present disclosure.

Fig. 10A and 10B illustrate a process for forming a conventional BAW filter.

Detailed Description

In the following description, for purposes of explanation, specific details are set forth in order to provide an understanding of the present disclosure. It will be apparent, however, to one skilled in the art that the present disclosure may be practiced without these specific details. Furthermore, those skilled in the art will recognize that the embodiments of the disclosure described below can be implemented in numerous ways, such as a process, an apparatus, a system, a device, or a method on a tangible computer readable medium.

The components or nodes shown in the figures are illustrative of exemplary embodiments of the disclosure and are intended to avoid obscuring the disclosure. It should also be understood that throughout the discussion, components may be described as separate functional units that may have sub-units, but those skilled in the art will recognize that various components or portions thereof may be divided into separate components or may be integrated together, including in a single system or component. It should be noted that the functions or operations discussed herein may be implemented as components. The components may be implemented in software, hardware, or a combination thereof.

Further, one skilled in the art will recognize that: (1) certain steps may optionally be performed; (2) the steps may not be limited to the specific order set forth herein; (3) certain steps may be performed in a different order, including simultaneously.

The elements/components shown in the figures are illustrations of exemplary embodiments of the disclosure and are intended to avoid obscuring the disclosure. Reference in the specification to "one embodiment," "a preferred embodiment," "an embodiment," or "embodiments" means that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the disclosure, and may be included in more than one embodiment. The appearances of the phrases "in one embodiment," "in an embodiment," or "in various embodiments" in various places in the specification are not necessarily all referring to the same embodiment or embodiments. The terms "comprising", "including" and "comprising" are to be construed as open-ended terms, and any list below is exemplary and not meant to be limiting to the listed items. Any headings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description or the claims. Furthermore, certain terminology is used in various places throughout the specification for the purpose of description and should not be construed as limiting.

Fig. 1-7 illustrate an exemplary process for forming a BAW filter according to an embodiment of the disclosure. As shown in fig. 1, a stack 100 of layers may include: a piezoelectric layer 104, a passivation layer 106, and a pseudo wafer 108 are sequentially stacked on the substrate 102.

In an embodiment, the substrate 102 may be a semiconductor substrate such as a silicon substrate. However, it will be apparent to those of ordinary skill in the art that the substrate 102 can be formed of other suitable materials as long as the piezoelectric layer 104 can be formed on the substrate 102.

In an embodiment, the piezoelectric layer 104 may be formed of a material having a piezoelectric effect. In an embodiment, the piezoelectric layer 104 may be formed of one or more of GaN, AlN, and ZnO, and deposited by a Metal Organic Chemical Vapor Deposition (MOCVD) method. It should be appreciated that other suitable deposition techniques may be used to form piezoelectric layer 104 depending on the materials of substrate 102 and piezoelectric layer 104.

Note that the MOCVD technique is an epitaxial growth technique, and therefore, the MOCVD technique can control the uniformity and thickness of the piezoelectric layer 104 better than the conventional sputtering technique. The thickness of the piezoelectric layer 104 can affect the resonant frequency characteristics of the BAW filter. Therefore, the piezoelectric layer 104 formed by the MOCVD technique can enhance the overall performance of the BAW filter. In an embodiment, the thickness of the piezoelectric layer 104 can be 10nm or less.

In an embodiment, the passivation layer 106 may protect the piezoelectric layer 104 from thermal and mechanical damage that may occur during BAW filter manufacturing. Moreover, if the pseudo wafer 108 is attached directly to the piezoelectric layer 104, a mismatch in the Coefficient of Thermal Expansion (CTE) between the piezoelectric layer 104 and the pseudo wafer 108 can create stress on the piezoelectric layer 104, thereby negatively affecting the performance of the piezoelectric layer 104. In an embodiment, the material and thickness of the passivation layer 106 may be selected to mitigate stress due to CTE mismatch. In an embodiment, the passivation layer 104 may be formed of polysilicon or silicon nitride.

In an embodiment, the dummy wafer 108 may provide mechanical support to other layers coupled thereto. In an embodiment, the dummy wafer 108 may be formed of silicon and affixed to the passivation layer 106 by being heated within a heating chamber. Note that other suitable methods may be used to secure the dummy wafer 108 to the passivation layer 106. For example, the dummy wafer 108 may be secured to the passivation layer 106 using an adhesive material.

As shown in fig. 2, substrate 102 may be removed from stack of layers 100 to expose a bottom surface of piezoelectric layer 104. The stack of layers can then be inverted, as shown in fig. 3, so that multiple layers can be formed on the piezoelectric layer 104. In an embodiment, the stack of layers 109 may comprise: a first metal layer 110, a passivation layer 111, a seed layer 112, and a diamond layer 114, which are sequentially formed on the exposed surface of the piezoelectric layer 104.

In an embodiment, the first metal layer 110 may be formed of a conductive metal such as Au, Ag, Ni, Ti, Al, or any combination thereof. Note that the first metal layer 110 may be formed using various manufacturing methods. In an embodiment, the first metal layer may be annealed to reduce the contact resistance between the first metal layer 110 and the piezoelectric layer 104.

In an embodiment, a passivation layer 111 may be formed on the first metal layer 110, wherein the passivation layer 111 may be formed of a dielectric material such as silicon nitride. In an embodiment, to form the seed layer 112, the stack of layers including layers 104, 106, 108, 110, and 111 may be immersed in an aqueous suspension of diamond nanoparticles (diamond seed particles) such that the top surface of the passivation layer 111 may be in direct contact with the aqueous suspension. The diamond particles may be adsorbed onto the surface of the passivation layer 111 to form the seed layer 112. Depending on the exposure time in the suspension and the concentration of diamond particles, the density of the particles in the seed layer 112 may be determined. Since the diamond particles may better adhere to the passivation layer 111 than the first metal layer 110, the passivation layer 111 may increase the particle number density of the seed layer 112.

In an embodiment, the passivation layer 111 may protect the first metal layer 110 and the piezoelectric layer 111 from thermal damage during the formation of the seed layer 112 and the diamond layer 114. In addition, the passivation layer 111 may electrically insulate the first metal layer 110 from the piezoelectric layer 111.

In an embodiment, the diamond layer 114 may also be formed by a Chemical Vapor Deposition (CVD) technique, even though other suitable techniques may be used. In an embodiment, the diamond seed particles in the seed layer 112 may act as seeds for the growth of the diamond layer 114. In an embodiment, the diamond layer 114 may be formed of a single crystal structure or a polycrystalline structure and provides mechanical support to the other layers in the stack of layers 109. Thus, the terms "diamond layer" and "diamond substrate" may be used interchangeably.

As shown in fig. 4, the pseudo wafer 108 and the passivation layer 106 may be removed from the stack of layers 109, thereby exposing the bottom surface of the piezoelectric layer 104. In an embodiment, grinding and/or etching methods may be used to remove both layers. Then, as shown in fig. 5, a second metal layer 116 may be formed on the piezoelectric layer 104.

In an embodiment, the second metal layer 116 may be formed of a conductive metal such as Au, Ag, Ni, Al, or Ti. Note that second metal layer 116 may be fabricated by any suitable wafer fabrication process. For example, a metal layer can be deposited on the piezoelectric layer 104, and the metal layer can be patterned using photolithographic techniques. The patterned metal layer may then be annealed to form second metal layer 116. The annealing process may reduce a contact resistance between the second metal layer and the piezoelectric layer.

In an embodiment, a portion of the piezoelectric layer 104 can be removed to form a patterned piezoelectric layer 104' and expose a portion of the first metal layer 110. The shape and size of the patterned piezoelectric layer 104' can determine the frequency range of the signal passing through the BAW filter. In embodiments, the piezoelectric layer may be patterned using any suitable wafer fabrication technique, such as a photolithographic technique.

In an embodiment, the metal pad 120 may be formed on the exposed portion of the first metal layer 110, as shown in fig. 7. In an embodiment, the metal pads 120 may be formed using any suitable wafer fabrication technique, such as a photolithographic technique. Fig. 8 shows a top view of BAW filter 130 according to an embodiment of the present disclosure.

In an embodiment, BAW filter 130 may function as a filter that allows signals in a particular frequency range to pass through and discriminates signals at other frequencies. In an embodiment, metal pad 120 may be coupled to one end of one wire 150 and second metal layer 116 may be coupled to one end of another wire 152. An input signal 162, which may include electrical signals of various frequencies, may be transmitted over conductor 152 and input to BAW filter 130. BAW filter 130 may pass some input electrical signal in a particular frequency range and transmit that signal as output signal 160 over conductor 150. Other input electrical signals discerned by BAW filter 130 may bounce back toward the other end of wire 152, as indicated by arrow 163, or be converted to thermal energy. In an embodiment, a DC bias voltage may be applied to the other end of the conductor 152 to enhance the performance of RF band filtering. The thermal energy may be conducted to the diamond layer (substrate) 114 and discharged to the outside of the BAW filter as indicated by arrow 164.

For illustrative purposes, in fig. 7, signals are input through conductor 152 and output through conductor 150. However, in some cases, signals may be input through conductor 150 and output through conductor 152, i.e., signals flow in the opposite direction to arrows 160 and 162. It should be noted that BAW filter 130 may operate in either signal flow direction.

For illustrative purposes, fig. 7 shows only one wire 150 directly connected to metal pad 120. However, it will be apparent to one of ordinary skill that more than one wire may be directly connected to the metal pad 120. Similarly, more than two wires may be directly coupled to second metal layer 116 to control the wire inductance. In an embodiment, a plurality of wires may be connected to the metal pad 120 in order to reduce wire inductance. Also, in embodiments, the spacing between the wires may be adjusted to control the wire inductance.

In an embodiment, metal pads 120, first metal layer 110, piezoelectric layer 104', and second metal layer 116 form an electrical path that allows electrical signals within a preset frequency range to pass therethrough and distinguish electrical signals outside the current frequency range. In an embodiment, the preset frequency range may be determined by various parameters, such as the shape, material, and/or size of each of the piezoelectric layer 104', the second metal layer 116, and the metal pads 120.

During operation, the BAW filter may generate thermal energy that needs to be discharged through the substrate to the outside of the BAW filter. If the thermal energy is not properly discharged, it may affect the resonant frequency, overall performance, and durability of the BAW filter. Unlike the conventional BAW filter having a substrate formed of a material with low thermal conductivity (e.g., silicon, gallium nitride, or glass), the BAW filter 130 includes a diamond layer (substrate) 114 having excellent thermal conductivity. Accordingly, the BAW filter 130 may effectively release thermal energy compared to a conventional BAW filter, and thus, the overall performance and durability of the BAW filter 130 will be less affected by the thermal energy during operation.

Fig. 9 shows a flow chart 400 of an exemplary process for manufacturing a BAW filter according to an embodiment of the invention. In step 402, a piezoelectric layer and a first passivation layer may be sequentially formed on a substrate. In an embodiment, the piezoelectric layer may be formed of a material having a piezoelectric effect, such as GaN, AlN, and ZnO, and deposited by a Metal Organic Chemical Vapor Deposition (MOCVD) method. It should be appreciated that other suitable types of deposition techniques may be used to form the piezoelectric layer depending on the materials of the first substrate and the piezoelectric layer. In an embodiment, the first passivation layer may be formed of a dielectric material such as polysilicon or silicon nitride and protects the piezoelectric layer from thermal and mechanical damage that may occur during the BAW filter manufacturing process.

At step 404, a dummy wafer (such as a silicon wafer) may be attached to the first passivation layer. In an embodiment, the dummy wafer may be attached to the first passivation layer by heating or using an adhesive material. In an embodiment, the first passivation layer may reduce stress due to CTE mismatch between the pseudo wafer and the piezoelectric layer.

At step 406, the substrate can be removed, thereby exposing a first surface of the piezoelectric layer. Then, at step 408, a first metal layer, a second passivation layer, a seed layer, and a diamond layer (substrate) may be sequentially formed on the exposed first surface of the piezoelectric layer. In an embodiment, the first metal layer may be formed of a conductive metal. In an embodiment, a first metal layer can be deposited on the exposed first surface of the piezoelectric layer. In an embodiment, the first metal layer may be annealed to reduce a contact resistance between the first metal layer and the piezoelectric layer. In an embodiment, the second passivation layer may be formed of a dielectric material such as silicon nitride. The second passivation layer may protect the first metal layer and the piezoelectric layer from thermal damage during formation of the seed layer and the diamond layer. Additionally, the second passivation layer may electrically insulate the first metal layer from the seed layer and the diamond layer.

To form the seed layer, a stack of layers including the diamond layer, the first passivation layer, the piezoelectric layer, the first metal layer, and the second passivation layer may be immersed in an aqueous suspension of diamond nanoparticles (diamond seed particles) such that a surface of the second passivation layer may be in direct contact with the aqueous suspension. In an embodiment, diamond seed particles may be adsorbed onto a surface of the second passivation layer to form a diamond seed layer. The number density of particles in the seed layer may be determined based on the exposure time in the suspension and the concentration of diamond particles. The second passivation layer may increase the particle count density of the seed layer since the diamond particles may adhere to the second passivation layer better than the first metal layer. In an embodiment, the diamond layer (substrate) may be grown on the seed layer by a CVD technique.

At step 410, the dummy wafer and the first passivation layer may be removed to expose the second surface of the piezoelectric layer. Then, at step 412, a second metal layer may be formed on the exposed second surface of the piezoelectric layer, the second metal layer being formed of a conductive metal. In an embodiment, the second metal layer may be formed by depositing and patterning a metal layer and annealing the patterned metal layer.

At step 414, a portion of the piezoelectric layer can be removed to expose a portion of the first metal layer. In an embodiment, a portion of the piezoelectric layer can be removed using a suitable etching technique. Then, at step 416, metal pads may be formed on the exposed surfaces of the first metal layer. In embodiments, the metal layer may be deposited and patterned using suitable techniques. In an embodiment, the patterned metal layer may be annealed in order to reduce the contact resistance between the metal pad and the first metal layer.

As discussed above in connection with fig. 10A and 10B, in a conventional BAW filter, a portion 1010 of the silicon substrate 1002 needs to be removed so that the first metal layer 1006 and the second metal layer 1008 are in direct contact with the piezoelectric layer 1004. In conventional systems, such an etching process is necessary because of the low acoustic wave velocity of silicon. In contrast, unlike the manufacturing process of the conventional BAW filter, in the embodiment of the present disclosure, the entire portion of the substrate 102 may be removed after attaching the dummy wafer 108 to the passivation layer 106, avoiding the conventional etching process, thereby reducing the manufacturing cost.

In an embodiment, since the diamond layer (substrate) 114 has high thermal conductivity, thermal energy generated during the operation of the BAW filter 130 may be effectively discharged to the outside of the BAW filter. Thus, the operating characteristics of the BAW filter are less affected by thermal energy than a conventional BAW filter having a substrate formed of a conventional substrate material such as silicon, sapphire, or glass.

One or more of the processes described in connection with fig. 9 may be performed by computer software. It should be noted that embodiments of the present disclosure can also relate to computer products having a non-transitory tangible computer-readable medium with computer code thereon for performing various computer-implemented operations. The media and computer code may be those specially designed and constructed for the purposes of the present disclosure, or they may be of the kind known or available to those having skill in the relevant art. Examples of tangible computer-readable media include, but are not limited to: magnetic media such as hard disks, floppy disks, and magnetic tape; optical media such as CD-ROMs and hologram devices; a magneto-optical medium; and hardware devices that are specially configured to store or store and execute program code, such as Application Specific Integrated Circuits (ASICs), Programmable Logic Devices (PLDs), flash memory devices, and ROM and RAM devices. Examples of computer code include machine code, such as produced by a compiler, and files containing higher level code that are executed by a computer using an interpreter. Embodiments of the disclosure may be implemented, in whole or in part, as machine-executable instructions, which may be in program modules, executed by a processing device. Examples of program modules include libraries, programs, routines, objects, components, and data structures. In a distributed computing environment, program modules may be located in both local and remote locations.

Those skilled in the art will recognize that no computing system or programming language is critical to the practice of the present disclosure. Those skilled in the art will also recognize that many of the elements described above may be physically and/or functionally divided into sub-modules or combined together.

While the invention is susceptible to various modifications and alternative forms, specific examples thereof have been shown in the drawings and are herein described in detail. It should be understood, however, that the invention is not to be limited to the particular forms disclosed, but to the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the scope of the appended claims.