The present invention relates to a semiconductor electronic device operable in radio frequencies (RFs), in particular, the invention relates to an electronic device having transmission lines.
An RF apparatus usually implements transmission lines, such as micro-strip line, to carry high frequency signals. Transmission lines within the RF apparatus may be connected with external devices through pads, and those pads are connected with the external devices through bonding wires, bumps, and the like. One type of electronic devices has developed and become popular in the field, in which a circuit board mounts amplifiers capable of outputting high power, which is called as a power amplifier module.
The transmission lines are usually matched in impedance thereof with that of units or blocks connected thereto, while, pads in an end of a transmission line is not matched or unable to be matched in impedance thereof with those units or blocks, which results in a reflection of high frequency signals at the pads. In particular, reflection of a signal becomes extreme in high frequencies of microwaves and millimeter waves.
An aspect of the present invention relates to a radio frequency (RF) apparatus that amplifies an RF signal. The RF apparatus of the invention includes a semiconductor chip and an assembly base that mounts the semiconductor chip thereon in upside down arrangement of a ball grid array. The semiconductor chip includes a semiconductor substrate, first to third metal layers, a top metal layer, a signal line, and a stub line. The semiconductor substrate includes a semiconductor active device therein. The first to third metal layers are stacked on the semiconductor substrate in this order and electrically isolated to each other by an insulating layer. The top metal layer, which is provided on a top surface of the insulating layer, includes a top ground layer and a pad that is electrically isolated from the top ground layer by a gap. The pad is connected with the assembly base through a solder ball of the ball grid array. The signal line carries the RF signal to the semiconductor active device or extracts the RF signal from the semiconductor active device. The stub line, which is also connected to the pad, has a length shorter than λ/4, where λ is a wavelength of the RF signal. A feature of the RF apparatus of the present embodiment is that the inner ground layer overlaps with the gap between the pad and the top ground layer, thereby increasing capacitive components to the pad.
The foregoing and other purposes, aspects and advantages will be better understood from the following detailed description of a preferred embodiment of the invention with reference to the drawings, in which:
Next, embodiment according to the present invention will be described as referring to accompanying drawings. In the description of the drawings, numerals or symbols same with or similar to each other will refer to elements same with or similar to each other without duplicating explanations.
The semiconductor chip 10 of the present embodiment provides a semiconductor substrate 12 and an insulating layer 14 that buries a metal layer 16 therein, a top metal layer 18 in a top surface thereof, and a via 15 passing at least a portion of the insulating layer 14. The via 15, which is filled with a metal, connects the metal layer 16 with the top metal layer 18.
The metal layer 16 includes a signal line 34 that is connected with a semiconductor active device formed in the semiconductor substrate 12, which is not illustrated in
The metal layer 16 includes a stub line 38 whose one end is connected with the pad 36 through a stacked via 17c, while the other end is connected with the top ground layer 32 through another stacked via 17d. Thus, the stub line 38 also overlaps with the top ground layer 32 as interposing the insulating layer 14 therebetween.
The semiconductor chip 10 thus configured is mounted on an assembly base 20 that provides a substrate 22, a metal layer 28 on a top surface of the substrate 22 and a ground layer 26 in a back surface of the substrate 22. The metal layer 28 includes a ground layer 42, a pad 46, and a signal line 44. The assembly base 20 further provides vias 25 each filled with a metal, where the vias 25 electrically connect the ground layer 42 on the top surface of the substrate 22 with the ground layer 26 in the back surface. The metal layer 28 on the top surface is protected with a cover layer 24. The signal line 44 forms a transmission line 43 type of micro-strip line by overlapping with the ground layer 26 in the back surface of the substrate 22.
Referring to
Symbols H12 to H28 appearing in
A feature of the embodiment is that the semiconductor chip 10 provides an additional ground layer 37, which is denoted by a hatched area in
The first metal layer 16b includes the signal line 34 and the stub line 38. The second metal layer 16c includes the inner ground layer 37, the third metal layer 16d includes the signal line 34d and the stub line 38d that is pulled out from the pad 36. The stacked via 17b connects the signal line 34 in the first metal layer 16b with the signal line 34d in the third metal layer 16d; the stacked via 17d connects the stub line 38 in an end thereof with the stub line 38d; the stacked via 17c connects the stub line 38d pulled out from the pad 36 with an end of the stub line 38 in the first metal layer 16b; and the stacked via 17d connects the other end of the stub line 38 with the top ground layer 32. The stacked vias, 17b and 17c, include the first and second via metals, 15b and 15c, and the second metal layer 16c; while, the stacked via 17d includes the first to third via metals, 15b to 15d, and the second and third metal layers, 16c and 16d. The inner ground layer 37 overlaps with the signal line 34d and the pad 36 as interposing the insulating layer 14c therebetween.
As
The stub line 38, which overlaps with the top ground layer 32, is connected in on end thereof with the pad 36 through the stacked via 17c and the other end thereof is connected with the top ground layer 32 through the stacked via 17d. Thus, the stub line 38 operates as a short stub. Because the stacked vias, 17c and 17d, are short enough compared with the length of the stub line 38, the short stub thus configured has the length substantially equal to the length of the stub line 38, and the stub line 38 in the length thereof is set to be shorter than λ/4, where λ is a wavelength of an RF signal subject to the present RF apparatus. Thus, the stub line 38 may be regarded as an inductor for the RF signal. Assuming that the pad 36 causes parasitic capacitance of Cpad against the top ground layer 32 and the stub line 38 has inductance of Lstub, total capacitance Ctotal of the pad 36 against the top ground layer 32 becomes:
Ctotal=Cpad−1/(ω2×Lstub).
Accordingly, the total capacitance viewed from the pad 36 becomes variable depending on the length of the stub line 38. The stub line 38 may compensate impedance mismatch between the transmission line 33 and the pad 36.
Because the short stub is formed in the stub line 38 and the top ground layer 32; the adjustment of the length of the stub line 38 becomes simple compared with arrangements where a short stub is formed by the top metal layers, 18 and 28, on the semiconductor chip 10 and the assembly base 20. Gaps between the pads, 36 and 46, and the ground layers, 32 and 42, are unable to be optionally deter mined and substantially restricted from a process for forming the bump 30. That is, a preset space is inevitably secured around the bump 30, which means that a stub line is unable to be drawn directly from the pad, 35 or 45. When the stub line 38 is provided in one of the first to third metal layers, 16b to 16d, the stub line 38 may be placed close enough to the pad 36.
An S-parameter S11 is evaluated for the arrangement of the RF apparatus according to the first embodiment shown in
As
According to the first embodiment, the inner ground layer 37, which is formed within in the insulating layer 14, overlaps with the signal line 34d in a portion of the gap 35, also with the pad 36 in a portion closer to the signal line 34. Accordingly, this arrangement between the pad 34 and the signal line 34d against the inner ground layer 37 may add additional capacitive components to the pad 36 and the signal line 34d, and improve the impedance matching between the transmission line 33 and the pad 36.
The inner ground layer 37 is connected with the top ground layer 32 in respective sides thereof that sandwiches the signal line 34d therebetween. This arrangement of the signal line 34d, the inner ground layer 37, and, as
The stub line 38 may have a length longer than λ/12 but shorter than 3λ/12 to suppress the reflection at the pad 36 and the bump 30. Or, further preferably, the stub line 38 has a length of λ/6, where λ is a wavelength of the RF signal subject to the RF apparatus of the invention. The stub line 38 is preferably formed in a side opposite to the signal line 34 with respect to the pad 36. Also, the stub line 38 preferably makes an angle greater than 90° against the signal line 34.
The third modification of the inner ground layer 37C is also not overlapped with the pad 36, and has a portion further penetrating under the top ground layer 32. The inner ground layers, 37 to 37C, of the embodiment and the modifications thereof may overlap with the signal line 34d in the portion of the gap 35 and a portion of the pad 36 in the side of the signal line 34d. Those arrangements of the inner ground layers, 37 to 37C, may add capacitive components to the pad 36, and the reflection performance of the pad 36 and the signal lines, 34 and 34d, maybe improved.
Thus, the signal line 34 may have a portion overlapped with the top ground layer, where the portion has an expanded width, which may increase capacitance added to the pad 36.
The fourth embodiment of the present invention relates to a monolithic microwave integrated circuit (MMIC) implementing the semiconductor chips, 10 to 10F, described above.
The semiconductor substrate 10 provides a semiconductor active device 50 and signal lines, 34a and 34b, to provide an RF signal to be amplified and to extract an amplified RF signal. The semiconductor active device 50 may be, for instance, a type of high electron mobility transistor (HEMT) having an InGaAs channel layer and an AlGaAs electron supply layer. The semiconductor active device 50 may be, in an alternative, a field effect transistor (FET). The semiconductor substrate 12 may be made of insulating material, such as sapphire, on which a semiconductor active device is formed.
The insulating layer 14 in the top surface thereof provides the top ground layer 32 and two pads, 36a and 36b, electrically isolated from the top ground layer 32 by the gaps, 35a and 35b. The signal lines, 34a and 34b, and the stub lines, 38a and 38b, are extracted from the pads 36a and 36b, along directions opposite to each other. Ends of the stub lines, 38a and 38b, opposite to the pads, 36a and 36b, are connected with the top ground layer 32 through the stacked vias 17d. The stub lines, 38a and 38b, have length shorter than λ/4, where λ is a wavelength of the RF signal subject to the RF apparatus. The inner ground layer, 37a and 37b, overlap with the pads, 36a and 36b, the gaps, 35a and 35b, and the signal lines, 34a and 34b, exactly, portions of the signal lines, 34a and 34b, in the third metal layer 16d. The pad 36a is an input pad to provide the RF signal to the semiconductor active device 50, while, the pad 36b is an output pad to extract the amplified RF signal.
The pad 36a is fixed onto the pad 46a on the assembly base 20 through the bump 30a, while, the pad 36b is connected to the pad 46b also on the assembly base 20 through the bump 30b. The bumps 30, which may be made of solder balls, constitute, what is called, the ball grid array.
Although the RF apparatus of the fourth embodiment shown in
The bumps, 30a and 30b, mounted of the pads, 36a and 36b, increase capacitive components against the top ground layer 32, which enhances the reflection of the RF signal. The inner ground layers, 37a and 37b, and the short stubs, 36a and 36b, may effectively suppress the reflection of the RF signal.
While particular embodiment of the present invention have been described herein for purposes of illustration, further modifications and changes will become apparent to those skilled in the art. Accordingly, the appended claims are intended to encompass all such modifications and changes as fall within the true spirit and scope of this invention.
The present application claims the benefit of priority of Japanese Patent Application No. 2016-213399, filed on Oct. 31, 2016, which is incorporated herein by reference.
Number | Date | Country | Kind |
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2016-213399 | Oct 2016 | JP | national |
This application is a continuation of and claims priority from U.S. application Ser. No. 15/797,944 filed on Oct. 30, 2017, which claims priority from Japanese Application 2016-213399 filed on Oct. 31, 2016, both applications being incorporated by reference herein.
Number | Date | Country | |
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Parent | 15797944 | Oct 2017 | US |
Child | 17105492 | US |