Note: Descriptions are shown in the official language in which they were submitted.
200910~
The present invention relates to a microwave integrated
circuit (IC) used for processing a microwave or millimeter
wave signal having a very high frequency of several GHz or
higher.
Recently, along with the rapid progression of IC
techniques, microwave ICs tend to hold an important place in
microwave circuits. In such a microwave IC, a circuit having
a function of impedance conversion or filtering is
constituted by a distributed constant line such as a
microstrip line obtained by adhering a metal thin film on a
semiconductor substrate.
In the conventional microwave IC, it is convenient if
characteristics of the distributed constant line can be
externally and electrically adjusted after the manufacture of
an IC.
For example, in order to obtain a maximum gain in an IC
constituting an amplifier, it is necessary to add an
impedance matching circuit for impedance-converting a
characteristic impedance (50 n) of an externally connected
microstrip line into a conjugate complex S11* of an S
parameter Sll of an amplification FET. However, FETs suffer
from variations in manufacture, and hence, the S parameter
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2009~ûS
also varies. Therefore, a standardized matching circuit
cannot realize designed performance. The same also applies
to an output matching circuit.
The present invention provides a microwave IC wherein a
line formed of a Schottky metal is formed as a distributed
constant line, and a semiconductor layer contacting the
Schottky metal line and an ohmic metal electrode contacting
the semiconductor conductive layer are arranged.
In a microwave IC, a distributed constant line is formed
by depositing or plating a metal thin film on a semiconductor
substrate, and its film thickness is about 1 to 10 ~m. The
electrical characteristics of the distributed constant line
are mainly determined by the frequency of a signal to be
processed, and the width and length of the line itself.
In the present invention, a Schottky diode is formed
between a Schottky metal line and a semiconductor conductive
layer. If the semiconductor conductive layer is assumed to
have an n conductivity type, when a DC potential of the
semiconductor conductive layer is lower than that of line, a
forward-biased current flows from the line side toward the
semiconductor conductive layer side. Otherwise, no current
flows. Therefore, the effective length of the distributed
constant line can be changed by a DC potential externally app
2009405
lied to the semiConductor conductive layer through the ohmic
metal electrode.
The present invention will become more fully understood
from the detailed description given hereinbelow and the
accompanying drawings which are given by way of illustration
only, and thus are not to be considered as limiting the
present invention.
Further scope of applicability of the present invention
will become apparent from the detailed description given
herei~after. However, it should be understood that the
detailed description and specific examples, while indicating
preferred embodiments of the invention, are given by way of
illustration only, since various changes and modifications
within the spirit and scope of the invention will become
apparent to those skilled in the art from this detailed
description.
Fig. 1 is a plan view showing an embodiment of the
present invention; and
Fig. 2 is a plan view showing another embodiment of the
present invention.
Length control of a short (short-circuiting) stub will
be explained below with reference to Fig. 1. A Schottky
metal line 12 and ohmic metal electrodes 13 and 14 are formed
on a semiconductor substrate 11.
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1 Semiconductor conductive layers 15 and 16 are formed on
a surface portion of the semiconductor substrate 11.
The semiconductor conductive layers 15 and 16 are formed
such that their one-end portions contact the Schottky
metal line 12 and their other-end portions contact the
ohmic metal electrodes 13 and 14. Schottky diodes are
formed at regions 17 and 18 where the Schottky metal
line 12 overlap the semiconductor conductive layers 15
and 16, and ohmic contacts are formed at regions 19 and
20 where the ohmic metal electrodes 13 and 14 overlap
the semiconductor conductive layers 15 and 16. Note
that the ohmic metal electrodes 13 and 14 respectively
comprise lead portions 13A and 14A and pad portions 13B
and 14B.
In this embodiment, GaAs is used as a material of
the semiconductor substrate 11. The semiconductor
conductive layers 15 and 16 have an n conductivity type
by doping Si ions in the substrate 11. The Schottky
metal line 12 has a three-layered structure of Ti/Pt/Au,
and the ohmic metal electrodes 13 and 14 has a two-
layered structure of AuGe/Ni.
Since the conductive layers 15 and 16 have the n
conductivity type, a short-circuit portion of a short
stub constituted by the Schottky metal line 12 changes
in a case (1) wherein a DC potential lower than that of
the Schottky metal line 12 is applied to the pad portion
14B and in a case (2) wherein the DC potential of the
2o094~5
1 pad portion 14B is set to be higher than that of the
Schottky metal line 12, and instead, a DC potential
lower than that of the Schottky metal line 12 is applied
to the pad portion 13B. In the case (1), an effective
length as the short stub is decreased by as compared
to that in the case (2).
More specifically, in the case (1), a short stub
extending from the region 18 to the ohmic metal
electrode 14 via the semiconductor conductive layer 16
is formed. In the case (2), a short stub extending from
the region 17 to the ohmic metal electrode 13 via the
semiconductor conductive layer 15 is formed.
Therefore, a line of a portion which will require
adjustment later is formed by the Schottky metal line
beforehand, and is connected to the ohmic metal
electrode through the semiconductor conductive layer.
Thus, the characteristics of the line can be externally
adjusted by increasing/decreasing a DC potential applied
to the semiconductor conductive layer through the ohmic
metal electrode after the manufacture of an IC.
When DC potentials to be applied to the pad portions
13B and 14B are set to be higher than that of the
Schottky metal line 12, an open stub can be formed.
In the above embodiment, when three or more sets of
the semiconductor conductive layers 15 and 16 and the
ohmic metal electrodes 13 and 14 are formed, the length
of the short stub can be changed in three or more steps.
2~94()5
1 Note that DC components and high-frequency signal
components can be discriminated from each other, and a
DC potential set to adjust the length of the line does
not adversely influence signals.
Materials used in the above embodiment are merely
examples, and the present invention is no limited to
this.
For example, as a material of the substrate, InP may
be employed. Ions to be doped to form an n-type
semiconductor conductive layer in a GaAs substrate
include Se, Sn, Te, and the like in addition to Si.
Fig. 2 is a plan view showing another embodiment of
the present invention. In this embodiment, a
semiconductor conductive layer 23 is formed to cross a
Schottky metal line 22 formed on a semiconductor
substrate 21 at two positions, and is connected to an
ohmic metal electrode 24. In this case, Schottky diodes
are also formed on regions 25 and 26. Thus, the length
of a line can be adjusted by setting a higher or lower
DC potential to be applied from the ohmic metal
electrode 24 to the semiconductor conductive layer 23
than that of the Schottky metal line 22.
More specifically, when the DC potential to be
applied to the ohmic metal electrode 24 is set to be
lower than that of the Schottky metal line 22, the
Schottky metal line 22 and the semiconductor conductive
layer 23 are electrically connected to each other on
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both the regions 25 and 26. For this reason, new line for
effectively short-circuiting the regions 25 and 26 lS formed.
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