Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Magnetic field
Reexamination Certificate
2001-06-27
2003-02-25
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Magnetic field
C257S422000, C257S108000, C257S659000
Reexamination Certificate
active
06525385
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims benefit of priority under 35 USC 119 to Japanese Patent Application No. P2000-194570 filed on Jun. 28, 2000, the entire contents of which are incorporated by reference herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device with an inductance element.
2. Description of Related Art
Conventional inductance elements are of core type or of shell type and employ combinations of coils and magnetic materials. These types of inductance elements became prevalent over monolithic inductance elements formed on ICs because the monolithic inductance elements i) must be bulky if required inductance is large and ii) must employ magnetic materials that are unsuitable for IC processes.
The reason why the inductance elements employ magnetic materials is because, when the inductance elements are energized, the magnetic materials effectively use magnetic flux to increase inductance.
Recent ICs, however, operate at high frequencies and require low inductance. Due to this and to make devices compact, there are requirements of integrally forming inductance elements on ICs or fabricating multi-chip modules including inductance elements.
To form inductance elements on ICs, it is preferable to make the inductance elements with flat coils such as a meander coil of
FIG. 1A and a
spiral coil of FIG.
1
B. Compared with multilayer coils, the flat coils involve ignorable contact resistance or via resistance and are easy to design.
FIG. 2
is a sectional view showing a resin-sealed semiconductor-device having an inductance element. This device has a conductive bed
101
, a mount
102
laid on the bed
101
, and a semiconductor chip
103
fixed to the mount
102
. A principal plane of the chip
103
has the inductance element
104
made of a spiral coil.
FIG. 3
is an enlarged view showing the inductance element
104
on the chip
103
. Electrodes of the chip
103
are connected to leads
106
through bonding wires
105
. The chip
103
, leads
106
, and wires
105
are consolidated with resin
107
into a package with the leads
106
partly extending outside.
The problem of this semiconductor device will be explained. In
FIG. 3
, the spiral coil (inductance element)
104
is formed on the semiconductor chip
103
. When current is passed, the coil
104
generates magnetic flux perpendicularly to the coil
104
as shown in
FIG. 4
that shows equi-vector potential lines representing the magnetic flux. When the coil
104
is operated at a high frequency by passing high-frequency current through the coil
104
, the direction of magnetic flux generated by the coil
104
changes at the current frequency. If a conductor
301
is arranged in the vicinity of the coil
104
, the magnetic flux from the coil
104
generates eddy current in the conductor
301
, to decrease the inductance of the coil
104
.
In
FIG. 2
, the semiconductor chip
103
is mounted on the conductive bed
101
, to form a standard semiconductor package. The distance between the coil
104
and the bed
101
is substantially equal to the thickness of the chip
103
. Namely, the inductance element, i.e., the coil
104
is in the vicinity of a conductor, i.e., the bed
101
at the distance defined by the thickness of the chip
103
.
FIG. 5
is a graph showing a relationship, between inductance provided by an inductance element operated at 10 MHz and the distance of the inductance element from a Cu conductor. The inductance element is a coil of 4000 &mgr;m in diameter, 80 &mgr;m in wire width, 80 &mgr;m in wire interval, 10 in turns, and 19 &mgr;m in thickness. The Cu conductor has a thickness of 0.15 mm. As the distance between the coil and the Cu conductor shortens, the inductance decreases. If the distance becomes 0.6 mm or shorter, the inductance decreases at the rate of the first power of the distance.
In
FIG. 2
, the bed
101
is a conductor and is close to the inductance element
104
at the distance defined by the thickness of the chip
103
. This thickness is thin to deteriorate the inductance of the inductance element
104
, as is apparent from FIG.
5
. If the thickness of the chip
103
is 0.29 mm, a designed inductance value will decrease to 69%.
SUMMARY OF THE INVENTION
The present invention is to provide a semiconductor device capable of reducing eddy current produced in a bed and securing required inductance. A semiconductor device according to this invention includes a semiconductor chip, an inductance element of flat structure formed above a first surface of the semiconductor chip, and a magnetic material formed below a second surface of the semiconductor chip opposite to the first surface. The semiconductor device according to the present invention has a magnetic material formed on the semiconductor surface opposite to the inductance element.
REFERENCES:
patent: 5068714 (1991-11-01), Seipler
patent: 5572478 (1996-11-01), Sato et al.
patent: 5939772 (1999-08-01), Hurst et al.
patent: 6097080 (2000-08-01), Nakanishi et al.
Inoue Tetsuo
Ito Takao
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Tran Long
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