INTEGRATED CIRCUIT DEVICE HAVING STRIP LINE STRUCTURE THEREIN

Abstract: An integrated circuit device (1) includes at least one semi­ conductor chip (3) having a plurality of circuit elements; a pack­ age (21 to 24) enclosing the semiconductor chip with a her­ metic seal; and a strip line unit (15-2, 11-1b, 11-2, 20 and 23 : 15-1, 11-1, 11-2, 11-3, 12-1 and 20) for connecting the circuit elements in the semiconductor chip to circuitry outside the package. The stripline unit has a microstrip line structure and a triplate strip line structure serial-connected to the micro­ strip line structure and connecting the outside circuits. The triplate strip line structure has a characteristic impedance equal to that of the microstrip line structure so that the strip line unit satisfies the required impedance matching. A center of the conductive layer strip line of the triplate strip line structure has a smaller width than that of a microstrip line of the microstrip line structure to have a predetermined im­ pedance so that the triplate strip line structure has a same char­ acteristic impedance as that of the microstrip line structure.

Description: The present invention relates to integrated circuit devices including microwave transmission lines for use, for example, in circuits required to operate at high speeds. High speed semiconductor integrated circuit (IC) chips for use in optical or other data processing applications at rates of, for example, one giga-bit per second (1Gb/s) are commercially available. In such a device a plurality of circuit elements, such as transistors and resistors, are formed in a chip made of semiconductor material such as silicon (Si) or gallium-arsenide (GaAs), the semiconductor IC chip being hermetically sealed in a package, in the same way as for other semiconductor IC chips. At the high frequencies concerned, the connection (lead) lines of nominally resistive material between circuit elements in the device must be regarded not only as resistive components but also as inductive components, lines having both low resistance and low inductance being required for high speed signal transfer lines. On the other hand, lines having high inductance are required for power supply lines and low speed signal transfer lines, to improve isolation between different power sources and between the circuit elements in the device. In high speed IC devices, impedance matching of the connection lines is also required: thus conventional line connection techniques used in well known ordinary semiconductor IC devices may be inapplicable. Accordingly, such a high-speed IC device is provided with a stacked layer structure comprising a plurality of vertically stacked composite layers, each composite layer consisting of an insulation layer on which a plurality of conductive strips are formed in a layer-form conductive pattern, and connection members embedded in the stacked layers in a direction perpendicular to the planes of the stacked layers. The IC chip in which the circuit elements are formed is mounted on the top of the stacked layers and hermetically sealed in a package. Connections between circuit elements in the IC device are made by means of the connection members and the conductive strips in the layer structure. The above requirement for impedance matching should be also applied to external connection lines between the high speed IC device and other high speed IC devices or other high speed operation circuits. Accordingly, triplate strip lines or microstrip lines are used for such external connection lines. However, in the prior art, connections between triplate strip lines and microstrip lines can suffer from the disadvantage of poor impedance matching, as will be described alter with reference to a specific example. In particular, the above-mentioned poor impedance matching may cause unacceptable degradation of the performance of high speed IC devices at operating speeds of greater than one giga-bit per second. According to the present invention, there is provided an integrated circuit device comprising a semiconductor chip, having a plurality of circuit elements, enclosed within hermetically sealed packaging means and connected to an external terminal of the device by means of a microstrip transmission line, within the said packaging means, connected in series with a triplate transmission line; characterised by a first insulating layer provided on one main surface thereof with a first layer-form pattern of conductive material, a second insulating layer having one main surface in contact with the said first pattern of conductive material and provided on its opposite main surface with a second layer-form pattern of conductive material, a third insulating layer having one main surface in contact with the said second pattern of conductive material and provided on its opposite main surface with a third layer-form pattern of conductive material, and a fourth insulating layer having one main surface in contact with the said third pattern of conductive material and provided on its opposite main surface with a fourth layer-form pattern of conductive material, each of the said first, second, third and fourth layer-form patterns consisting of at least one conductive strip; and further characterised in that the said microstrip transmission line is constituted by a strip portion of the said fourth pattern together with respective adjacent portions of the said fourth insulating layer and the said third pattern, one terminal of the said semiconductor chip being connected to the microstrip transmission line at one end of the said strip portion of the fourth pattern, the other end of that strip portion being connected by way of a conductor passing through the said third and fourth insulating layers to one end of a strip portion of the second pattern, the other end of which is connected to an external terminal of the device, the said triplate transmission line being constituted by the said strip portion of the said second pattern together with respective adjacent portions of the said third conductive layer and the said third insulating layer and the said second insulating layer and the said first conductive layer, and the width of the said strip portion of the said second pattern, measured parallel to the main surface of the said second insulating layer, being smaller than that of the said strip portion of the said fourth pattern, so that the characteristic impedance of the said triplate transmission line is substantially equal to that of the said microstrip transmission line. Such a device has the worthwhile advantage that different portions of a common layer are used to provide respective parts of the microstrip and triplate transmission lines, thereby producing a device structure that is compact, efficient in its use of materials, and relatively easy to construct. Reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1a shows a sectional view of a part of a prior integrated circuit (IC) device taken along the line X-X' in Figure 1b; Figure 1b shows a plan view of the IC device taken along the line H-H' in Figure 1a; Figure 2 shows a sectional view of an IC device embodying the present invention; Figure 3a shows a plan view of a part of the IC device shown in Figure 2, indicated by a reference A₁ and taken along the line H-H' in Figure 2; Figure 3b shows a sectional view of the IC device taken along the line Y-Y' in Figure 3a; Figure 4 shows a perspective view of a part of the IC device shown in Figure 2 and indicated by reference B. Referring to Figures 1a and 1b, an IC device includes a semiconductor IC chip 3 having a semiconductor substrate of Si or GaAs on which a plurality of transistors and other circuit elements are formed, mounted on an insulation layer 32 of ceramic or the like. The IC device also includes a stacked layer structure consisting of a conductive wire strip 31 formed on the insulation layer 32 and further consisting of a metal film 34 placed beneath the insulation layer 32 and mounted on another insulation layer 36. The IC device further includes a package including an insulator 33 and a metal cap 35. A hermetically sealed cavity 20', wherein the IC chip 3 is located, is defined by the package and the stacked layer structure. The conductive wire strip 31 is connected to a terminal of the IC chip 3 by soldering 37. The conductive wire strip 31 extends outside the IC device through a hermetic seal portion and is soldered to a connection wire 39 on a substrate 38 positioned outside and adjacent to the IC device. Accordingly, the conductive wire strip 31 functions as an external connection wire. Another conductive wire strip 31-1 (Figure 1b) can also be provided. In Figure 1a, the conductive wire strip 31 may have, at a portion indicated by reference A ' / 1, a microstrip line structure, because the metal film 34 is provided beneath the conductive wire strip 31 and separated therefrom by the insulation layer 32, and the cavity 20' is provided above the conductive wire strip 31. In addition, another portion of the conductive wire strip 31, indicated by reference A ' / 2, may be a balanced-type strip line structure, i.e. a triplate strip line structure, because the conductive wire strip 31 is enclosed between the metal cap 35 and the metal film 34 by the insulator 33 and the insulator layer 32, both the insulator 33 and the insulating layer 32 having the same thickness d₀ and same dielectric constant ε. Note that the thickness t₀ and width W₀ of the conductive wire strip 31 are identical at portions indicated by references A ' / 1 and A ' / 1. For example, when the dielectric constant ε = 10. the insulation thickness d₀ = 330 µm, the conductive wire strip thickness t₀ = 15 µm, and the conductive wire strip width W₀ = 300 µm, the characteristic impedance Z₀ at the portion indicated by reference A ' / 1 is 50Ω, which is a desired characteristic impedance in the example. However, a different characteristic impedance Z ' / 0 of approximately 33Ω will be obtained at the portion indicated by reference A ' / 2 due to the dielectric effect of the insulator 33. As a result, a mismatching between the respective characteristic impedances of the microstrip and the triplate line structures occurs and brings about a reflection loss. Preferred embodiments of the present invention will now be described. Referring to Figure 2, an IC device 1 embodying the present invention includes a package 2, the package 2 consisting of a cap 21 formed of an insulation material, an upper shield 22 formed of an insulation material, a seal layer 23, and a side wall 24 formed of an insulation material. The IC device 1 further comprises an IC chip 3, including a plurality of circuit elements formed on a semiconductor substrate of Si or GaAs, and a stacked layer unit 11. The IC chip 3 is mounted on the top of the stacked layer unit 11 and is located in a hermetically sealed cavity 20 defined by the package 2 and the stacked layer unit 11. The above-mentioned insulation material is typically a dielectric material. The IC device 1 is mounted on a printed circuit board 52 through conductive leads 51 and is secured to a plate 53 through a stud 54 having one end fixed to a bottom surface 11-6C of the stacked layer unit 11, the shaft of the stud 54 passing through a hole 56 in the printed circuit board 52 and the plate 53, and the other end of the stud 54 being fastened to the plate 53 by a nut 55. The stacked layer unit 11 includes six stacked layers 11-1 to 11-6. Each of the stacked layers 11-1 to 11-6 includes an insulation layer or a dielectric layer, as shown by the layer 11-1b for the upper layer 11-1, and a layer-form pattern of conductive material, as shown by the pattern 11-1a for the upper layer 11-1, which pattern consists of at least one conductive layer strip. The insulation layers 11-1b, etc., are formed of a sintered ceramic and have a thickness of approximately 300 um and a dielectric constant of 10. Two conductive wire strips 15-1 and 15-2 are also provided in the pattern 11-1a on the insulation layer 11-1b adjacent to the IC chip 3. The conductive layer strips of the second layer 11-2 are used for ground lines or power supply lines. The conductive layer strips of the fourth and sixth layers 11-4 and 11-6 are also used for ground lines or power supply lines. Conductive layer strips of the third layer 11-3 are used for high speed signal lines. The conductive layer strips of the fifth layer 11-5 are used for low speed signal lines. Figure 3a is a plan view of a part of the IC device denoted by references A ' / 1 and A ' / 2 in Figure 2 and taken along the line H-H' in Figure 2. Figure 3b is a sectional view of the IC device, taken along the line Y-Y' in Figure 3a. Figures 3a and 3b correspond respectively to Figures 1b and 1a discussed above. In Figures 2, 3a and 3b, the conductive wire strip 15-2 varies in width along its length and includes a relatively wide portion 15-2a, a relatively narrow portion 15-2b, and a further relatively wide portion 15-2c. The width W a of the wider portions 15-2a and 15-2c is 300 um and the width W b of the narrower portion 15-2b is 100 um. The thickness t of the conductive wire strip 15-2b is a uniform 15 um throughout the portions 15-2a to 15-2c. The length of the narrower portion 15-2b is identical to that of the seal layer 23. The conductive wire strip 15-2 functions as an external connection wire. One end of the wider portion 15-2a of the conductive wire strip 15-2 inside the IC device is connected to a terminal of the IC chip 3 through a wire 18-2 and the other end of the conductive wire strip 15-2 (i.e. the further wide portion 15-2c which lies outside the IC device and extends down the side wall 24) may be connected to other circuits in other IC devices. The further wide portion 15-2c may be formed as a co-planar strip line. The structure associated with the wide portion 15-2a of the conductive wire 15-2 and denoted by reference A₁ in Figure 2 is similar to that shown in Figure 1a and thus constitutes a microstrip line structure, because the conductive layer 11-2a formed on the insulation layer 11-2b of the second layer 11-2 is provided beneath the wide portion 15-2a and the cavity 20 is provided above the wide portion 15-2a. The insulation layer 11-2b between the wide portion 15-2a of the conductive wire strip 15-2 and the conductive layer 11-2a is (like the layer 32 of Figure 1a) also formed of a sintered ceramic and has a thickness of approximately 330 µm and a dielectric constant of 10. As a result, the characteristic impedance of the microstrip line structure is 50Ω. In addition, another structure, associated with the narrow portion 15-2b of the conductive wire strip 15-2 and denoted by reference A₂, includes the insulation layer 11-1b, the conductive layer 11-2a and the seal layer 23, which consists of an insulation layer 23b (formed of a sintered ceramic and having a thickness t₂₃ of approximately 330 µm, identical to the thickness t₁₁₋₁ of the insulation layer 11-1b, and a dielectric constant of 10) and a conductive layer 23a formed on the insulation layer 23b. The narrow portion 15-2b has a width Wb of 100 µm, which is narrower than that of the wide portion 15-2a. Capacitors are formed in the insulation layer 23b and the insulation layer 11-1b, so that the portion concerned has a triplate strip line structure. By providing the above-mentioned capacitors above and below the portion 15-2b, the width W b of the narrow width portion 15-2b may be reduced. In this triplate strip line structure, the width W b of the narrow width portion 15-2b (W b = 100 µm) is chosen so that any adverse effects due to the dielectric constant of the insulation layer 23b may be cancelled. As a result, the characteristic impedance of the triplate strip line structure is 50Ω, identical to that of the microstrip line structure described above. Accordingly the conductive wire strip 15-2 functions as an external connection wire which has impedance matching along its entire length, with the result that losses such as reflection loss do not occur. In the above embodiment, the principal requirement is to make the characteristic impedance of the triplate strip line structure, which is altered by the presence of the insulation layer 23b, equal to that of the microstrip line structure. More specifically, the capacitance of the narrow width portion 15-2b is set to a predetermined value so that impedance matching is achieved between the two structures. The characteristic impedance can be arbitrary, and could, for example, be 75Ω. Figure 4 is a perspective view of the IC device at the portion indicated by reference B in Figure 2. In Figures 2 and 4, the conductive wire strip 15-1, formed on the insulation layer 11-1b, is electrically connected to the conductive strip 11-3a, formed on the insulation layer 11-3b, by means of a viahole 14-1 consisting of electrically conductive material inserted into a throughhole 12-1 formed in the insulation layers 11-1b and 11-2b, in a direction perpendicular to the planes of those layers. A microstrip line structure is constituted by the conductive layer 11-2a, the insulation layer 11-1b, the conductive wire strip 15-1, and the cavity 20 above the conductive wire strip 15-1 in the same way as set forth with reference to Figures 3a and 3b. The thickness t₁ of the conductive wire strip 15-1 is 15 µm and the width W₁ is 300 µm, these dimensions being equal to those of the wide portion 15-2a of the conductive wire strip 15-2. The thickness and material of the insulation layer 11-1b are as mentioned above. Accordingly, the characteristic impedance of the structure associated with the conductive wire strip 15-1 is 50Ω. A triplate strip line structure is also constituted by the conductive layer 11-4a formed on the insulation layer 11-4b, the insulation layer 11-3b, the conductive strip 11-3a, the insulation layer 11-2b, and the conductive layer 11-2a in the same way as set forth with reference to Figures 3a and 3b. Capacitors CS₁ and CS₂ are formed in the insulation layers 11-2b and 11-3b. The thickness t₂ of the conductive strip 11-3a is identical to the thickness t₁ of the conductive wire strip 15-2, and the width W₂ is 100 µm, which is identical to the width W b in Figure 3a. By providing the capacitors CS₁ and CS₂ above and below the conductive strip 11-3a, the width W₂ may be reduced as described previously. The thickness and material of the insulation layer 11-3b are identical to those of the insulation layer 11-2b. The width W₂ is smaller than the width W₁, and accordingly the triplate strip line structure has a characteristic impedance of 50Ω identical to that of the microstrip line structure of the conductive wire strip 15-1, despite the effect of the dielectric constant of the insulation layer 11-2b, described above with reference to Figures 3a and 3b. In this embodiment, impedance matching between the microstrip line structure and the triplate strip line structure is achieved in the external connection line constituted by the conductive wire strip 15-1, the viahole 14-1 and the conductive layer 11-3a, with the result that losses such as reflection loss do not occur. Furthermore, because in this embodiment the conductive layer 11-2a provides both the upper conductive layer of the triplate strip line structure and the conductive base layer of the microstrip line structure, the IC device is compact, efficient in its use of materials, and relatively easy to construct. One end of this external connection wire is connected to a terminal of the IC chip 3 inside the IC device, and the other end outside the IC device is connected to a co-planar strip line 25 mounted on the surface of the side wall 24 as shown in Figure 2. Many widely different embodiments of the present invention may be constructed without departing from the spirit and scope of the present invention. It should be understood that the present invention is not limited to the specific embodiments described in this specification, except as defined in the appended claims.

Claims: An integrated circuit device comprising a semiconductor chip (3), having a plurality of circuit elements, enclosed within hermetically sealed packaging means (21 to 24) and connected to an external terminal (25) of the device by means of a microstrip transmission line, within the said packaging means, connected in series with a triplate transmission line; characterised by a first insulating layer (11-4b) provided on one main surface thereof with a first layer-form pattern (11-4a) of conductive material, a second insulating layer (11-3b) having one main surface in contact with the said first pattern of conductive material and provided on its opposite main surface with a second layer-form pattern (11-3a) of conductive material, a third insulating layer (11-2b) having one main surface in contact with the said second pattern of conductive material and provided on its opposite main surface with a third layer-form pattern (11-2a) of conductive material, and a fourth insulating layer (11-1b) having one main surface in contact with the said third pattern of conductive material and provided on its opposite main surface with a fourth layer-form pattern (11-1a) of conductive material, each of the said first, second, third and fourth layer-form patterns (11-4a, 11-3a, 11-2a, 11-1a) consisting of at least one conductive strip; and further characterised in that the said microstrip transmission line is constituted by a strip portion (15-1) of the said fourth pattern (11-1a) together with respective adjacent portions of the said fourth insulating layer (11-1b) and the said third pattern (11-2a), one terminal of the said semiconductor chip being connected to the microstrip transmission line at one end of the said strip portion (15-1) of the fourth pattern, the other end of that strip portion (15-1) being connected by way of a conductor (14-1) passing through the said third and fourth insulating layers to one end of a strip portion of the second pattern (11-3a), the other end of which is connected to an external terminal (25) of the device, the said triplate transmission line being constituted by the said strip portion of the said second pattern (11-3a) together with respective adjacent portions of the said third conductive layer (11-2a) and the said third insulating layer (11-2b) and the said second insulating layer (11-3b) and the said first conductive layer (11-4a), and the width of the said strip portion of the said second pattern (11-3a), measured parallel to the main surface of the said second insulating layer (11-3b), being smaller than that of the said strip portion (15-1) of the said fourth pattern (11-1a), so that the characteristic impedance of the said triplate transmission line is substantially equal to that of the said microstrip transmission line. A device as claimed in claim 1, wherein the said semiconductor chip (3) is connected to a further external terminal (15-2c) of the device by means of a further microstrip transmission line, within the said packaging means, connected in series with a further triplate transmission line that leads to the said further external terminal (15-2c). A device as claimed in claim 2, wherein the said packaging means includes a further layer-form insulating portion (23b) having one main surface in contact with the said fourth layer-form pattern of conductive material (11-1a) and provided on its opposite main surface with a further layer-form conductive portion (23a), and wherein the said further microstrip transmission line is constituted by a further strip portion (15-2a) of the said fourth pattern (11-1a) together with respective adjacent portions of the said fourth insulating layer (11-1b) and the said third pattern (11-2a), a second terminal of the said semiconductor chip being connected to the said further microstrip transmission line at one end of the said further strip portion (15-2a) of the fourth pattern, the other end of that further strip portion being directly connected to one end of an additional strip portion (15-2b) of the said fourth pattern (11-1a), which additional strip portion constitutes the central conductor of the said further triplate transmission line and is connected at its other end to the said further external terminal (15-2c) of the device, the other conductors of the said further triplate transmission line being provided respectively by the said further layer-form conductive portion (23a) and a portion of the said third pattern (11-2a), the width of the said additional strip portion (15-2b) as measured parallel to the main surface of the said fourth insulating layer (11-1b) being smaller than that of the said further strip portion (15-2a) of the said further microstrip transmission line so that the characteristic impedance of the said further triplate transmission line is substantially equal to that of the said further microstrip transmission line. A device as claimed in claim 1, 2 or 3, wherein the said semiconductor chip (3) is mounted on the said opposite main surface of the said fourth insulating layer (11-1b).

Inventors: EMORI, SHINJI, KITASAGAMI, HIROO SHIRAHATADAIJUTAKU 4-203, MIYAUCHI, AKIRA, NISHIMOTO, HIROSHI, OKIYAMA, TADASHI FUJIMISO 1261, SUGIMOTO, MASAHIRO, TAMADA, HARUO
Applicants: FUJITSU LIMITED
Application year: 1986
Main classification: H01P3
IPC codes: H01L23, H05K3, H05K1, H01P5