Air-bridge inductor structure, manufacturing method and application thereof

Abstract

The application discloses an air-bridge inductance structure, which comprises two metal layers, a first metal layer and a second metal layer, and the first metal layer and the second metal layer have annular bodies arranged in corresponding lower and upper intervals, and the annular bodies have a broken gap and a first pin and a second pin respectively, the two annular bodies are connected through an interlayer connecting part, the total number of turns between the first pin and the second pin is more than one turn and less than two turns; the second metal layer further comprises a plurality of first branches, which are extended radially outward from the outer periphery of the annular body and supported on the substrate through one-time bending; and the annular body of the second metal layer is covered with an insulating layer with a relative dielectric constant less than 5. The application improves the Q value of the inductor, and when applied to a filter, makes the insertion loss characteristic of the filter better and the frequency band attenuation characteristic better.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of semiconductors, and particularly relates to an air-bridge inductor structure, a manufacturing method and application. BACKGROUND

[0002] Inductors are important components of various circuits in modern communication systems. In integrated circuits, passive devices such as inductors and capacitors are usually integrated with active devices such as transistors on the same substrate to achieve specific functions. For example, a 5G filter chip is based on Integrated Passive Device (IPD) technology on a gallium arsenide substrate to manufacture inductors and capacitors for combination, forming an LC band-pass filter. The performance of inductors and other devices will affect the performance and application of the filter.

[0003] Inductor Q value: also known as the quality factor of inductance, is a main parameter for measuring inductor devices. It refers to the ratio of inductive reactance to equivalent loss resistance when an inductor works under an alternating voltage at a certain frequency. The higher the Q value of the inductor, the smaller the loss and the higher the efficiency. In the prior art, integrated inductors are usually formed by spiral inductor coils on the surface of a substrate using integrated circuit manufacturing processes. The inductance value is small, and under high frequency conditions, the magnetic flux of the inductor coil decreases, resulting in additional energy loss, which reduces the Q value (quality factor) of the entire inductor. Especially in the application of band-pass filters and other filters, it is necessary to obtain an inductor with a high Q value in an inductor with a small inductance. Therefore, it is of great significance to develop new structures to improve the Q value of inductors. SUMMARY

[0004] The application provides an air-bridge inductor structure, a manufacturing method and application to solve the problems in the prior art.

[0005] To achieve the above purpose, the technical scheme of the application is as follows:

[0006] An air-bridge inductor structure is provided on a substrate, comprising a first metal layer and a second metal layer; the first metal layer has a first annular body, and the second metal layer has a second annular body, which is spaced above the first annular body, and the first annular body and the second annular body each have a broken gap; the first metal layer has a first pin, and the second metal layer has a second pin; the first metal layer and the second metal layer are connected by a first interlayer connection part and a second interlayer connection part clamped between the first annular body and the second annular body, so that the total number of turns between the first pin and the second pin is more than one turn and less than two turns; the second metal layer further comprises a plurality of first legs, which are extended radially outward from the outer periphery of the second annular body and supported on the substrate by one bending; the second annular body is covered with an insulating layer, and the relative dielectric constant of the insulating layer is < 5.

[0007] Optionally, the thickness of the insulating layer is 1-20 μm.

[0008] Optionally, the insulating layer is a silicon dioxide layer with a thickness of 5-10 μm.

[0009] Optionally, the first annular body has a first notch, the first pin extends outward from one side of the first notch, and the first interlayer connection is located on the other side of the first notch; the second annular body has a second notch, the second pin extends outward from one side of the second notch, and the second interlayer connection is located on the other side of the second notch.

[0010] Optionally, the first pin and the second pin are located on opposite sides of the center of the first annular body.

[0011] Optionally, the first leg is composed of a horizontal extension and a pier portion, the horizontal extension extends radially outward from the outer periphery of the second annular body, and the pier portion extends vertically downward from the end of the horizontal extension to abut the substrate.

[0012] Optionally, the thickness of the horizontal extension is the same as the thickness of the second annular body; the length of the radial extension of the pier portion is 40%-70% of the length of the radial extension of the first leg.

[0013] Optionally, the length of the radial extension of the first leg is 16-22 μm; the length of the radial extension of the pier portion is 10-15 μm, and the thickness is 7-12 μm.

[0014] Optionally, the second metal layer further comprises a plurality of second legs, the second legs extend radially inward from the inner periphery of the second annular body and are supported on the substrate by one bend.

[0015] Optionally, the number of the second legs is less than the number of the first legs, or the length of the second legs is less than the length of the first legs.

[0016] Optionally, it further comprises a waterproof layer, which is wrapped on the outside of the first metal layer, the second metal layer, and the insulating layer.

[0017] A filter comprising a substrate and a filter circuit provided on the substrate, the filter circuit comprising an inductor and a capacitor, the inductor being an air-bridge inductor structure as described above.

[0018] A radio frequency module, comprising the filter as described above.

[0019] A method for manufacturing an air-bridge inductor structure, comprising the following steps:

[0020] 1) forming a first metal layer on a substrate;

[0021] 2) forming a sacrificial layer on the first metal layer and the substrate outside the first metal layer, so that the sacrificial layer forms two first regions exposing the first metal layer and several second regions exposing the substrate outside;

[0022] 3) forming a first interlayer connection, a second interlayer connection and a second metal layer by a local metal deposition process; wherein the first interlayer connection and the second interlayer connection are located in the first regions; the second metal layer includes a second annular main body located on the sacrificial layer, a second pin and a part of the first leg extending radially outward, and a part of the first leg bent and supported on the substrate in the second regions;

[0023] 4) forming an insulating layer on the second metal layer;

[0024] 5) removing the sacrificial layer.

[0025] The beneficial effects of the present application are:

[0026] 1) The structure of the air-bridge double-layer metal inductor is constructed, and a silicon dioxide layer is formed on the annular structure of the second metal layer, which on one hand reduces the eddy current effect, increases the Q value of the inductor, makes the insertion loss characteristic of the filter better when applied to the filter, the frequency band attenuation characteristic is better, and the filter specification is easy to achieve; on the other hand, as a protective layer, it increases the reliability of the front-end process;

[0027] 2) The structure design of the L-shaped leg provides support while reducing the generation of the sharp tip effect and the parasitic of the electric charge at the leg through the design of fewer corners, ensuring that more electric charges flow to the surface of the second annular copper layer, thereby improving the Q value;

[0028] 3) The adopted process has high reliability and good production yield. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 It is a schematic diagram of the overall structure of the air-bridge inductor structure of the embodiment;

[0030] Figure 2 It is a schematic diagram of the exploded structure of the air-bridge inductor structure of the embodiment;

[0031] Figure 3 It is a schematic diagram of the position relationship between the first leg and the first metal layer of the air-bridge inductor structure of the embodiment;

[0032] Figure 4 It is a schematic diagram of the structure of the air-bridge inductor structure of the embodiment covered with a waterproof layer;

[0033] Figure 5Circuit schematic diagram of the filter of the example;

[0034] Figure 6 Q value test spectrum of the example (silicon dioxide layer thickness = 10 um) and the comparative example (silicon dioxide layer thickness = 0 um);

[0035] Figure 7 Insertion loss characteristic curve diagram of the example (silicon dioxide layer thickness = 10 um) and the comparative example (silicon dioxide layer thickness = 0 um);

[0036] Figure 8 is a partial enlarged view of Figure 7 DETAILED DESCRIPTION

[0037] The present application will be further described below with reference to the drawings and specific examples. The drawings of the present application are only schematic and are non-limiting according to the scope of the present application, as the dimensions of the various features are intended to be explanatory rather than limiting. The relative dimensions of the various features in the drawings are not necessarily to scale, and the specific dimensions are not intended to be limiting. The definition of the relative positions of the various components in the drawings, and the front / back, up / down, right / left definitions are intended to be illustrative and not limiting, as the components can be rotated 180 degrees and the same components can be present.

[0038] Referring to Figure 1 and Figure 2 , an air-bridge inductor structure is provided on a substrate 1, which includes a first metal layer 2 and a second metal layer 3. The substrate 1 is, for example but not limited to, silicon, gallium arsenide, sapphire, spinel, polycrystalline alumina, glass, or the like with high impedance. The first metal layer 2 has a first annular body 21 with a first gap 21a, and the second metal layer 3 has a second annular body 31 with a second gap 31a, the second annular body 31 is provided above the first annular body 21 with an air layer 5 formed therebetween. The first metal layer 2 has a first pin 22, and the second metal layer 3 has a second pin 32, the first metal layer 2 and the second metal layer 3 are connected through a first interlayer connection 4a and a second interlayer connection 4b clamped between the first annular body 21 and the second annular body 31, so that the total number of turns between the first pin 22 and the second pin 32 is more than one turn and less than two turns. The second metal layer 3 further includes a plurality of first legs 33, the first legs 33 are extended radially outward from the outer periphery of the second annular body 31 and supported on the substrate 1 by one-time bending. The upper surface of the second annular body 31 is covered with a silicon dioxide layer 6 as an insulating layer.

[0039] ​Specifically, the first pin 22 is formed by the first annular body 21 extending outwardly at one side of the first gap 21a, and the first interlayer connection 4a is located at the other side of the first gap 21a. The second pin 32 is formed by the second annular body 31 extending outwardly at one side of the second gap 31a, and the second interlayer connection 4b is located at the other side of the second gap 31a. In the embodiment, the first annular body 21 and the second annular body 31 are arranged oppositely, and in the direction perpendicular to the surface of the substrate 1, the first annular body 21 and the second annular body 31 are located at the same position, that is, the inner and outer edges of the annular body coincide in the top view, and the external connection is made through the first pin 22 and the second pin 32. The first pin 22 and the second pin 32 are located at the opposite sides of the center of the annular body, that is, the first pin 22 and the second pin 32 take the center of the annular body as the center, and the included angle is 180°. Thus, the first layer from the first pin 22 to the second interlayer connection 4b and the second layer from the second interlayer connection 4b to the second pin 32 are connected in series, the first layer and the second layer between the first interlayer connection 4a and the second interlayer connection 4b are connected in parallel, and the number of turns of the inductor formed is about 1.5. The first annular body 21 and the second annular body 31 are reversely arranged in the gap and the leading direction, that is, 180°, which has the most smooth current flow path and the least impact on charge loss.

[0040] Reference Figure 3 In order to arrange the first annular body 21 and the second annular body 31 in parallel and form a stable air layer 5 in the middle, a plurality of first legs 33 are arranged on the outer periphery of the second annular body 31 to provide support, the first leg 33 does not contact the first annular body 21, and is composed of a horizontal extension 331 and a pier column 332 vertically extending downward from the end of the horizontal extension 331 to abut the substrate 1, the pier column 332 is a vertical column, forming an L-shaped structure.

[0041] The first leg 33 has only one corner formed by one bending, and the corner has the same height as the second annular body 31 and has a large distance from the substrate surface, which on the one hand reduces the charge concentration caused by the corner tip effect and leads to the charge loss of the inductor metal layer; on the other hand, it avoids the corner close to the substrate surface and makes the charge flow through the substrate, which leads to the charge loss of the inductor metal layer; through the above two aspects, the charge loss of the inductor metal layer is avoided, and the Q value is further improved.

[0042] Specifically, the corner tip will generate a tip effect, which is a phenomenon that the tip part of the same charged conductor has a larger surface charge density than the smooth part, the electric field strength near the tip is stronger, and the tip is easy to discharge to the surrounding air or the adjacent ground body. The concentration of electric charge on the tip will make the electric charge of the inductive metal layer less. The first leg 33 of the embodiment has only one corner formed by one bending, and the corner is flush with the surface of the second annular body 31, which maximizes the loss of electric charge caused by the tip effect under the premise of providing good support. In addition, since the electric charge will concentrate on the metal surface, the pier part 332 is a vertical column structure with the shortest distance, and the parasitic electric charge on the pier is less, and the electric charge will flow to the second layer of metal surface more, which improves the Q value.

[0043] The radial length BP1 and the thickness BP2 of the first leg 33 are set to be as small as possible under the premise of playing a supporting effect. Preferably, the horizontal extension part 331 is horizontally extended outward from the second annular body 31, and the thickness is the same as that of the second annular body 31 to facilitate synchronous deposition with the second annular body 31 in the process. The radial length BP3 of the pier part 332 is 40% to 70% of the radial length BP1 of the first leg 33, so as to leave a gap with the sidewall of the first annular body 21. Through the above structural arrangement, the parasitic electric charge in the first leg 33 is reduced, and the electric charge flows to the surface of the second annular body 31 as much as possible to obtain a better Q value.

[0044] For example, the outer diameter of the first annular body 21 and the second annular body 31 is 200 to 300 μm, the line width is 30 to 80 μm, the thickness of the first annular body 21 is 2 to 5 μm, and the thickness of the second annular body 31 is 3 to 8 μm. Preferably, the thickness of the second annular body 31 is greater than the thickness of the first annular body 21. The thickness of the air layer 5 and the first interlayer connecting part 4a and the second interlayer connecting part 4b is the same, and the thickness is 1 to 2 μm. The thickness BP2 of the first leg 33 is equal to the sum of the thicknesses of the first annular body, the second annular body and the air layer. The radial length of the horizontal extension part 331 (i.e. the radial length BP1 of the first leg 33) is 16 to 22 μm, and the radial length BP3 of the pier part 332 is 10 to 15 μm.

[0045] The first leg 33 is arranged symmetrically along the center of the second annular body 31 on the opposite sides to make the support force on both sides uniform. Further, the second leg 32 is also supported on the substrate 1 by one bending to provide support characteristics and stable connection characteristics.

[0046] To further improve the supporting effect, the second metal layer 3 is further provided with a second leg 34 extending radially inward at the inner periphery of the second annular body 31. The second leg 34 has a similar structure as the first leg 33 and is also supported on the substrate 1 by one-time bending. The length (defined as the circumferential length) of the second leg 34 is smaller than that of the first leg 33 and the number of the second leg 34 is less than that of the first leg 33 to reduce the impact on the Q value.

[0047] The silicon dioxide layer 6 is provided on the second annular body 31, which can reduce the eddy current formed by the adjacency effect, reduce the charge loss, and increase the Q value. In the embodiment, the silicon dioxide layer 6 covers the upper surface of the second annular body 31, and has an opening 6a corresponding to the second gap 31a. In other embodiments, the silicon dioxide layer can also have a complete annular structure. In other embodiments, the silicon dioxide layer can also partially cover the second annular body 31. In other embodiments, the silicon dioxide layer can also cover the side surface of the second annular body 31.

[0048] In addition, other insulating materials with a relative dielectric constant less than 5 are also suitable for use as the insulating layer of the present application.

[0049] Reference Figure 4 In addition, the air bridge inductance structure is further coated with a waterproof layer 7 on the outside. The waterproof layer is made of PI or dry film and is coated on the outside of the metal layer and the silicon dioxide layer 6 to prevent water vapor and foreign matter from entering the internal air layer 5.

[0050] Conventional photolithography process, metal deposition and silicon dioxide deposition process can be applied to the manufacture of the air bridge inductance structure of the present application. For example, a first metal layer can be formed on the substrate; a sacrificial layer is formed on the first metal layer and the substrate outside the first metal layer, so that the sacrificial layer forms two first regions exposing the first metal layer and a plurality of second regions exposing the outside substrate; a first interlayer connection, a second interlayer connection and a second metal layer are formed by a local metal deposition process; the first interlayer connection and the second interlayer connection are located in the first region; the second metal layer includes a second annular body on the sacrificial layer, a second pin and a portion of the first leg extending radially outward, and a portion of the first leg supported on the substrate in the second region; a silicon dioxide layer is formed by physical vapor deposition (PVD) method; then the sacrificial layer is removed to form an air bridge structure. Finally, the WLP process is used for packaging, and the PI layer is used to coat the metal inductance and the silicon dioxide layer as a waterproof layer.

[0051] The air bridge inductor structure is applied to a filter, and an LC circuit diagram of the filter is shown in FIG. 8. The filter has two terminals, and the two terminals are connected in series through a capacitor C9, a first resonator, a second resonator, and a capacitor C7 in sequence; a third resonator is connected between the first resonator and the second resonator, and the other end of the third resonator is connected in series with a capacitor C10 and grounded. The first resonator is formed by a capacitor C8 and an inductor L8 in parallel, the second resonator is formed by a capacitor C1 and an inductor L7 in parallel, and the third resonator is formed by a capacitor C4 and an inductor L6 in parallel. The values of the capacitors and the inductors in the resonators are related to the passband communication frequency and the bandwidth, and therefore the passband frequency and the bandwidth can be set by setting the values of the capacitors and the inductors in the resonators. Figure 5 The air bridge inductor structure is applied to a filter, and an LC circuit diagram of the filter is shown in FIG. 8. The filter has two terminals, and the two terminals are connected in series through a capacitor C9, a first resonator, a second resonator, and a capacitor C7 in sequence; a third resonator is connected between the first resonator and the second resonator, and the other end of the third resonator is connected in series with a capacitor C10 and grounded. The first resonator is formed by a capacitor C8 and an inductor L8 in parallel, the second resonator is formed by a capacitor C1 and an inductor L7 in parallel, and the third resonator is formed by a capacitor C4 and an inductor L6 in parallel. The values of the capacitors and the inductors in the resonators are related to the passband communication frequency and the bandwidth, and therefore the passband frequency and the bandwidth can be set by setting the values of the capacitors and the inductors in the resonators.

[0052] Q value simulation tests are performed on the air bridge inductor structures with different thicknesses of the silicon dioxide layer, and a structure without the silicon dioxide layer is taken as a comparative example, and the results are shown in Table 1 and FIG. 9. Figure 6 As shown in Table 1 and FIG. 9, at a frequency of 5 GHz, the Q value of the structure with a thickness of 10 um of the silicon dioxide layer is 4.86 more than that of the structure without the silicon dioxide layer, and the increase is 7.41%. When the thickness of the silicon dioxide layer is greater than 10 um and changes from 10 um to 20 um, the Q value does not change much and tends to be saturated. The silicon dioxide layer with a thickness of 5 um to 10 um can achieve a relatively ideal effect.

[0053] Table 1

[0054]

[0055] Reference Figure 7 and Figure 8 The insertion loss characteristic of the bridge inductor structure of the embodiment is improved by using a silicon dioxide layer with a thickness of 10 um. Compared with the structure without the silicon dioxide layer, the insertion loss of the structure with the silicon dioxide layer is increased from -0.229 to -0.215 at a frequency of 5 GHz, and the increase rate is 6.5%; the high-frequency attenuation frequency zero point is reduced from -29.184 to -30.231, and the reduction is about 3.58%. It can be seen that the bridge inductor structure is applied to the filter, and the insertion loss characteristic of the filter is improved.

[0056] Conventionally, a radio frequency front end module generally includes a band pass filter (BPF), a power amplifier (PA), a low noise amplifier (LNA), a TX filter, an RX filter, a frequency converter and the like. The radio frequency front end module is provided with a plurality of signal transmission paths, including a signal transmitting path and a signal receiving path. In each signal transmission path, by selecting a specific frequency band in the signal transmission path, the radio frequency signal of the specific frequency band, such as N77 or N79, can be processed. The application of the above bridge inductor structure to the band pass filter can make it easier to achieve the N79 specification of the 5G filter.

[0057] The above embodiments are only used to further illustrate the air bridge inductor structure and the manufacturing method of the present application, but the present application is not limited to the embodiments. Any simple modification, equivalent change and modification made according to the technical essence of the present application to the above embodiments all fall within the protection scope of the technical solutions of the present application.

Claims

1. An air-bridge inductor structure, characterized by: The inductance structure is arranged on a substrate and includes a first metal layer and a second metal layer. The first metal layer has a first annular body, and the second metal layer has a second annular body arranged above the first annular body. The first annular body and the second annular body each has a broken gap. The first metal layer has a first pin, and the second metal layer has a second pin. The first metal layer and the second metal layer are connected by a first interlayer connection and a second interlayer connection arranged between the first annular body and the second annular body. The total number of turns between the first pin and the second pin is more than one and less than two. The second metal layer further includes a plurality of first legs extending radially outward from the outer periphery of the second annular body and supported on the substrate by one-time bending. The second annular body is covered with an insulating layer having a relative dielectric constant less than 5. The first leg is composed of a horizontal extension extending radially outward from the outer periphery of the second annular body and a columnar portion vertically extending downward from the end of the horizontal extension to abut the substrate. The second metal layer further includes a plurality of second legs extending radially inward from the inner periphery of the second annular body and supported on the substrate by one-time bending.

2. The air-bridge inductor structure of claim 1, wherein: The thickness of the insulating layer is 1-20 μm.

3. The air-bridge inductor structure of claim 2, wherein: The insulating layer is a silicon dioxide layer having a thickness of 5-10 μm.

4. The air-bridge inductor structure of claim 1, wherein: The first annular body has a first gap, and the first pin extends outward from one side of the first gap. The first interlayer connection is located at the other side of the first gap. The second annular body has a second gap, and the second pin extends outward from one side of the second gap. The second interlayer connection is located at the other side of the second gap.

5. The air-bridge inductor structure of claim 4, wherein: The first pin and the second pin are located on opposite sides of the center of the first annular body.

6. The air-bridge inductor structure of claim 1, wherein: The thickness of the horizontal extension is the same as the thickness of the second annular body. The radially extending length of the columnar portion is 40%-70% of the radially extending length of the first leg.

7. The air-bridge inductor structure of claim 6, wherein: The radially extending length of the first leg is 16-22 μm. The radially extending length of the columnar portion is 10-15 μm, and the thickness is 7-12 μm.

8. The air-bridge inductor structure of claim 1, wherein: The number of the second legs is less than the number of the first legs, or the length of the second leg is less than the length of the first leg.

9. The air-bridge inductor structure of claim 1, wherein: A waterproof layer is further included, which is wrapped on the outside of the first metal layer, the second metal layer, and the insulating layer.

10. A filter, characterized by, A substrate and a filter circuit arranged on the substrate are included. The filter circuit includes an inductance and a capacitance. The inductance is an air bridge inductance structure as claimed in any one of claims 1-9.

11. A radio frequency front end module, comprising: A filter as claimed in claim 10 is included.

12. A method of fabricating the air-bridge inductor structure of claim 1, wherein, The following steps are included: 1) forming a first metal layer on a substrate; 2) forming a sacrificial layer on the first metal layer and the substrate outside the first metal layer, so that the sacrificial layer forms two first regions exposing the first metal layer and a plurality of second regions exposing the substrate outside; 3) forming a first interlayer connection, a second interlayer connection and a second metal layer by a local metal deposition process; wherein the first interlayer connection and the second interlayer connection are located in the first region; the second metal layer comprises a second annular main body located on the sacrificial layer, a second pin and a portion of the first leg extending radially outward, and a portion of the first leg located in the second region and supported on the substrate by bending; 4) forming an insulating layer on the second metal layer; 5) removing the sacrificial layer.

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