Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – For high frequency device
Reexamination Certificate
1999-08-05
2001-12-25
Wilson, Allan R. (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
For high frequency device
C257S678000, C257S729000, C257S730000
Reexamination Certificate
active
06333552
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to millimeter wave semiconductor devices used in a range of equal to or higher than the millimeter wave range.
2. Description of the Background Art
With the recent improvement and enhancement of information processing devices in speed, and image processing devices in resolution, there has been noted high-speed, large-capacity personal communications at radio frequencies such as a millimeter wave band having frequencies of 30 to 300 GHz, a centimetric-wave band or a quasi-millimeter wave band having frequencies close to 30 to 300 GHz.
For such communications it is necessary to make the most use of characteristics of radio waves as well as create a package adapted for radio frequencies which can be small in size and produced at reduced cost and which also require only a short period of time for development.
In general, radio-frequency (RF) packages tend to require sealing in view of the following three points: reduction of influences of unnecessary electromagnetic waves, maintenance of airtightness, and mechanical sealing. RF packages are mechanically sealed for the same reasons as general semiconductor packages. Sealing RF packages to maintain their airtightness is necessary because RF semiconductor chips in general tend to affect RF characteristics when humidity, temperature and the like vary.
To reduce influences of unnecessary electromagnetic waves, a factor which would not be considered for RF packages for relatively low frequencies such as mobile phones, Personal Handy-Phone System (PHS) is crucial in designing RF packages for millimeter wave frequencies and frequencies close thereto.
More specifically, in a millimeter wave-band range, a wavelength is 1 to 10 millimeters long in the atmosphere, and an effective wavelength would be approximately 100 microns to several millimeters when the dielectric constant of a material forming a package is taken into consideration. Since this length corresponds to a scale for a size of a RF semiconductor chip, a package or a RF circuit, its three-dimensional geometry and material properties such as dielectric constant, dielectric loss, significantly affect RF characteristics of the RF package. Thus the three-dimensional configuration internal to the package is an important factor in designing it.
FIG. 6
shows an exemplary configuration of a conventional RF package. Such RF packages are disclosed, for example, in Japanese Patent Laying-Open Nos. 08-018001 and 10-079623.
In this RF package, a RF semiconductor chip
30
with a RF circuit
32
formed on a semiconductor substrate
31
is fixed on an upper surface of a wiring substrate
10
via conductive paste
61
. Chip
30
is fixed faceup, i.e., a surface thereof opposite to the surface bearing RF chip circuit
32
faces wiring substrate
10
. Chip RF circuit
32
is connected via a wire
41
to a RF substrate circuit
12
of wiring substrate
10
. The space in which RF semiconductor chip
30
is provided on wiring substrate
10
is sealed by a metal cap
57
for shielding electromagnetic waves.
FIG. 7
shows another exemplary configuration of a conventional RF package. It differs from the
FIG. 6
configuration in that RF semiconductor chip
30
is connected to RF substrate circuit
12
of wiring substrate
10
via a bump
40
such that a surface bearing RF chip circuit
32
faces wiring substrate
10
, i. e., facedown.
The
FIG. 6
example, however, does not give any consideration to how the size of the space sealed by the cap affects electromagnetic-wave resonance and the like. Consequently, a large number of waveguide modes are created in the space at an frequency band applied and unnecessary electromagnetic waves leaking from RF chip circuit
32
, RF substrate circuit
12
, wire
14
and other components cause a large number of resonance in the space, resulting in significantly degraded RF characteristics.
Particularly, wire
41
can be a major cause of unnecessary electromagnetic waves, since it is difficult for wire
41
to achieve RF-matching due to its high inductance. Furthermore, with RF semiconductor chip
30
mounted faceup, the opposing cap's conductor can affect RF chip circuit
32
, wire
41
and other components and change their transmission characteristics and the like.
In general the
FIG. 7
conventional example generates less unnecessary electromagnetic waves than the
FIG. 6
conventional example, since RF semiconductor chip
30
is mounted facedown via bump
40
. However, as well as the
FIG. 6
conventional example, this conventional example also fails to give consideration as to how the size of the space sealed by the cap affects electromagnetic-wave resonance and the like and a large number of waveguide modes will tend to be created in the space at a frequency band applied. Consequently, unnecessary electromagnetic waves leaking from the RF chip circuit, the RF substrate circuit and other components cause a large number of resonance in the space, resulting in significantly degraded RF characteristics.
The generation of waveguide modes provides a transmission characteristic for small loss and high energy. Thus even if a device with unsealed desirable RF characteristics has been obtained, the RF characteristics will significantly change when the device is sealed. In some cases, no RF characteristics may be obtained, and electromagnetic waves propagated through the space can affect and cause active elements to oscillate and emit heat so that the RF semiconductor chip may be destroyed. Even if it is not significantly degraded, it is necessary to design the RF circuit so that the changed characteristics after the device is sealed are desired characteristics. However, waveguide modes change depending on the arrangement of the RF semiconductor chip and chip parts for matching in the sealed space, the design of the RF substrate circuit, and the like. Accordingly, reviews and modifications are often required in designing a device and this extends the period for development of the device and increases the cost for designing the device.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a miniaturized millimeter wave semiconductor device having a sealing structure capable of electromagnetic shielding, wherein the device has a configuration which exhibit good RF characteristics in a space sealed by a conductive cap for electromagnetic shielding and also introduces reduced RF-characteristic variations caused between before and after the device is sealed so as to allow the device to be readily applied to a variety of packages associated with various product types. Further, the device does not require a long period for development nor high cost.
A millimeter wave semiconductor device of the present invention that achieves the above objective is comprised of a millimeter wave device, a wiring substrate with the millimeter wave device mounted thereto, and a sealing cap including a conductor on a surface thereof for sealing the millimeter wave device. The sealing cap has a ground potential at the conductor provided on a surface thereof and the sealing cap has a form which reduces waveguide modes created in a sealed space for a frequency band applied.
As a specific dimension to reduce the creation of waveguide modes, the spacing between an upper surface of the wiring substrate and an internal surface of the sealing cap is set to less than one fourth of a spatial wavelength of a frequency applied.
In accordance with the present invention, such a configuration can suppress the generation of a multitude of waveguide modes and reduce mutual effects between the sealing cap and each of the wiring substrate and the millimeter wave device, and enhance absorption of unnecessary electromagnetic waves. Thus better RF characteristics can be obtained and they also vary little from the time before to the time after the device is sealed so thus the period for the development and the designing cost can be reduced. These characteristics resulting from the above configuration can be sign
Kakimoto Noriko
Suematsu Eiji
Sharp Kabushiki Kaisha
Wilson Allan R.
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