Wave transmission lines and networks – Coupling networks – Frequency domain filters utilizing only lumped parameters
Reexamination Certificate
2000-10-13
2003-07-08
Bettendorf, Justin P. (Department: 2817)
Wave transmission lines and networks
Coupling networks
Frequency domain filters utilizing only lumped parameters
C333S175000
Reexamination Certificate
active
06590473
ABSTRACT:
CLAIM OF PRIORITY
This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from my application THIN-FILM BAND PASS FILTER AND METHOD FOR MANUFACTURING IT filed with the Korean Industrial Property Office on Oct. 15, 1999 and there duly assigned Ser. No. 1999/44752
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a bandpass filter that filters an input electrical signal to pass only signals in a specific frequency band, and more particularly to, a thin-film bandpass filter in which a spiral inductor and a capacitor are formed in a thin-film shape, and a manufacturing method thereof.
2. Description of the Related Art
In general, bandpass filters use a principle that impedance in combination of an inductor and a capacitor changes depending on a frequency. In other words, since a resonant frequency f
0
equals
1
2
π
L
C
when an inductor L and a capacitor C are connected in series, a filter for passing only signals of a specific frequency band may be embodied by repeating the arrangement of the inductor L and the capacitor C. As a filter operated within the range of a microwave frequency of 500 MHz or higher, a thin-film microwave bandpass filter, as shown in
FIG. 1
, has been proposed. The thin-film bandpass filter consists of a plurality of capacitors
32
formed by appropriately stacking and arranging a metal layer and an insulating layer on a planar substrate
12
, a plurality of spiral inductors
10
, and electrical connection. In this case, the spiral inductors
10
and capacitors
32
are electrically connected in series, alternately, by a lead pattern, and the spiral inductors
10
are disposed at the ends. As shown in
FIG. 2
, each capacitor
32
includes a pair of first metal layers
34
and
36
which are separated by a predetermined gap G on the planar substrate
12
, an insulating layer
40
formed on at least a portion of the top surface of the first metal layers
34
and
36
, a second metal layer
42
overlapping the first metal layers
34
and
36
and formed on the top surface of the insulating layer
40
.
As shown in
FIGS. 1 and 3
, each spiral inductor
10
is formed in a spiral shape and including first and second traces
22
and
24
comprised of first metal layers
16
and
18
formed on the planar substrate
12
, a connection bridge
28
comprised of a second metal layer
18
, overlying the first metal layers
16
and
18
and connecting between the first and second traces
22
and
24
, and an insulating layer
20
for insulating the intersection portion.
The first trace
22
is looped into a coil and ends at an interior end
26
. The second trace
24
is disposed parallel and adjacent to the periphery of the first trace
22
. The connection bridge
28
contacts the interior end
26
of the first trace
22
while being connected to the second trace
24
across an intermediate portion
30
of the first trace
22
. In this case, the insulating layer
20
isolates the connection bridge
28
from the intermediate portion
30
of the coiled trace. Reference numerals
1
and denote contact pads. The thin-film bandpass filter described above has a structure in which the spiral inductors
10
and the capacitors
32
are alternately connected in series between the contact pads
1
and
5
.
Since the conventional thin-film bandpass filter has a two-dimensional structure in which the inductors are attached to the substrate
12
, a parasitic capacitance is generated between the inductors
10
and the substrate
12
to a great extent, and accordingly, the Q factor of the inductor
10
is reduced. Therefore, the conventional bandpass filter has smaller resonant frequency of the inductor
10
itself. Accordingly, the inductor
10
is of a narrower range for use. Also, the insertion loss of the bandpass filter is increased. Thus, the conventional thin-film bandpass filter has a drawback in that a process of amplifying a signal that passes through the filter is further required. Furthermore, there is another problem in that the overall size of the bandpass filter is large since inductors and capacitors are connected in series with the plane substrate
12
unfolded. However, when such a bandpass filter is implemented on a semiconductor chip, the filter consumes a large amount of precious space. In addition, the inductor may contain a parasitic capacitance which is unwanted. Furthermore, the insertion loss of the filter may be high, there may be a low resonant frequency, and the cost for manufacturing the bandpass filter may be excessive.
What is needed is a design for a bandpass filter implemented on a semiconductor chip, that is small, has a low manufacturing cost, low insertion loss, a higher resonant frequency, and eliminates the problem of parasitic capacitances.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an improved design and an improved method of manufacture of a thin film bandpass filter.
It is also an object of the present invention to provide a bandpass filter that is space efficient. It is yet another object of the present invention to provide a bandpass filter that is easy and inexpensive to manufacture.
It is still an object of the present invention to provide a thin film bandpass filter that has a low insertion loss.
It is still yet another object of the present invention to provide a thin film bandpass filter that reduces and eliminates parasitic capacitances.
It is yet also an object of the present invention to provide a semiconductor bandpass filter that has a higher resonant frequency.
Accordingly, to achieve the above object, the present invention provides a thin-film bandpass filter including: a substrate; a plurality of first capacitors formed on the substrate, each being electrically connected in series; at least one second capacitor electrically connected to branch terminals positioned between the plurality of first capacitors; an inductor electrically connected in parallel to the second capacitor; and a plurality of supports for propping up the inductor so that the inductor is separated a predetermined space above the substrate and/or the second capacitor. The first and second capacitors, respectively, include a first metal layer, a dielectric layer, and a second metal layer, all of which are sequentially formed on the substrate. The inductor is comprised of a predetermined pattern of a thin-film metal layer propped by the plurality of supports, to both ends of which are electrically connected to the first and second metal layers of the second capacitor, and suspended by the substrate and/or the second capacitor.
Furthermore, the inductor includes a spiral inductor portion having at least one turn, formed in a flat spiral shape above the supports and propped by the supports; a first connecting portion for electrically connecting an interior end of the spiral inductor portion and one metal layer of the second capacitor, the first connection portion including a vertical portion extending downward from the interior end of the spiral inductor portion, and a horizontal portion extending from one side of the vertical portion to be separated from the spiral inductor portion; and a second connecting portion for electrically connecting an exterior end of the spiral inductor portion and the other metal layer of the second capacitor, the second connection portion including a vertical portion extending downward from the exterior end of the spiral inductor portion. In this case, preferably, at least a portion of the supports are formed on the second capacitor and at least a portion of the spiral inductor portion of the inductor is positioned above the second capacitor.
The present invention also provides a method of manufacturing a thin-film bandpass filter including the steps of: preparing a substrate; sequentially providing a first metal layer, a dielectric layer and a second metal layer at predetermined positions on the substrate to form a plurality of first capacitors, ea
Kim Duck-Su
Seo O-Gweon
Bettendorf Justin P.
Bushnell , Esq. Robert E.
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