Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1998-03-10
2001-09-11
Picard, Leo P. (Department: 2835)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S360000, C257S361000, C257S362000
Reexamination Certificate
active
06288428
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device provided with a driver for supplying an electric current to a circuit that includes an inductance such as a stepping motor, and particularly to a semiconductor integrated circuit device for use in a disk drive apparatus.
2. Description of the Prior Art
As an example of such a semiconductor integrated circuit device, a description will be given on a semiconductor integrated circuit device for processing a head movement drive signal as well as to-be-recorded and read-out signals in a disk drive apparatus. This semiconductor integrated circuit device is provided with a stepper block for supplying an electric current to a stepping motor to move a magnetic head, a logic section for reading and writing data from and to a magnetic disk through the magnetic head, a signal path for connecting the logic section to a signal input pad, and a protection circuit for protecting the inside circuitry against a surge voltage that may be applied to the pad from outside. The protection circuit is usually composed of two diodes connected in series between the power source voltage and ground, with the node between them connected to the signal path (to the pad).
The stepper block has an output circuit that is composed of, for example, a first and a second transistor, both being of the NPN type. The first transistor has its collector connected to the power source voltage, and the second transistor has its emitter connected to ground. The emitter of the first transistor and the collector of the second transistor are connected via an output pad to the coil of the motor. Both transistors receive a drive voltage at their base. If the above-mentioned protection circuit is provided near this output circuit, the logic section may malfunction for the following reason. The current supplied to the stepping motor causes the inductance of the stepping motor to produce back electromotive force, which then makes the collector voltage of the second transistor lower than the ground level. This turns on the protection diode that is formed nearby, and thus causes the logic section to erroneously recognize receipt of, for example, a low-level signal and output a false control signal.
Next, a description will be given, with reference to
FIG. 6
, as to why the protection diode is turned on when the collector voltage of the second transistor becomes lower than the ground level. As shown in
FIG. 6
, on a P-type semiconductor substrate
69
, P-type, N-type, insulating, and other layers are formed by impurity diffusion, epitaxial growth, or a similar method in the following manner. For a protection diode
54
, an N
+
layer
70
is provided on the substrate
69
, and, on top of this N
+
layer
70
, an N layer
73
is provided. In addition, another N layer
71
is provided through the N layer
73
. The two N layers
71
and
73
are of different concentration.
The N layer
71
is connected via an aluminum deposit
72
to a pad
58
. Part of the N layer
73
is put in contact with a P layer
75
so that a PN junction of the diode is formed. The P layer
75
is connected via an aluminum deposit
81
to ground (GND).
Part of the N layer
73
is separated by an insulator
76
. The P layer
75
is also provided with an insulator
77
. In addition, insulating layers
78
to
80
are provided on the top surface for the separation of the aluminum deposits
72
and
81
.
On the other hand, as an NPN-type transistor
131
a
for the output circuit of the stepper block, an N
+
layer
85
is provided, as an embedding, on the P-type substrate
69
. On top of this N
+
layer
85
, an N
−
layer
87
is provided. Another N
+
layer
86
is provided through the N
−
layer
87
so as to contact the N
+
layer
85
, and, Ad on top of the N
+
layer
86
, an N layer
82
is provided.
The N layer
82
is connected via an aluminum deposit
88
to a pad
125
, which is intended to be connected to the stepping motor. The symbol L represents the inductance component included in the stepping motor. The N layer
82
serves as the collector (C) terminal of the transistor
131
a.
An insulator
95
is provided in the N
−
layer
87
to separate the N
+
layer
86
and the N layer
82
from a P layer
90
. The P layer
90
includes, as part of itself, a P
+
layer
89
. An N
+
layer
91
is provided in the P layer
90
so as not to contact the P
+
layer
89
. The P
+
layer
89
and the P layer
90
serve as the base (B) of the transistor
131
a
, and are connected via a deposit
92
to a control circuit
33
a.
The N
+
layer
91
serves as the emitter (E) of the transistor
131
a
, and is connected via an aluminum deposit
93
to ground (GND). Insulators
94
to
96
and
76
are oxide films provided for the separation of circuit elements, and P layers
101
,
102
, and
75
are diffusion layers provided also for the separation of circuit elements. Insulating layers
78
to
80
and
97
to
100
are provided for the separation of deposits
88
,
92
, and
93
.
Now, suppose that the inductance (L) of the stepping motor
2
has produced back electromotive force, thereby making the voltage at the collector (C) of the transistor
131
a
lower than the ground (GND) level.
In particular, when the voltage at the collector (C) of the transistor
131
a
is lower than the ground (GND) level by more than about 0.7 V (the forward voltage V
F
), the parasitic transistor
60
(of the NPN type) hidden in the semiconductor integrated circuit device produces leak currents I
1
and I
2
, which are approximately equal to each other, and these currents turn on the protection diode
54
. As a result, as described previously, the logic section, by erroneously recognizing receipt of a low-level signal, is led to malfunction.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a semiconductor integrated circuit device that operates stably without causing malfunctioning of an input/output protection circuit.
To achieve the above object, according to the present invention, in a semiconductor integrated circuit device intended for use in a magnetic recording apparatus and provided with a driver for supplying an electric current to a circuit including an inductance, a pad for receiving or outputting a signal from or to outside, and a protection diode connected to the pad, the pad is disposed near the drive in the protection diode is disposed at a predetermined distance from the driver.
In this construction, the pad is disposed near the driver, and the protection diode is disposed sufficiently away from the driver. The pad and the protection diode are connected by aluminum deposition or a similar method. The driver is connected to a circuit including an inductance such as a stepping motor. Even if the inductance produces back electromotive force, the placement of the protection diode away from the driver helps reduce the resulting leak currents to zero or, if any, negligibly low levels.
REFERENCES:
patent: 5493133 (1996-02-01), Duvvury et al.
patent: 5656952 (1997-08-01), McCall et al.
patent: 5805396 (1998-09-01), Sado et al.
patent: 6169311 (2001-01-01), Iwasaki
patent: 6204537 (2001-03-01), Ma
Arent Fox Kintner & Plotkin & Kahn, PLLC
Duong Hung Van
Picard Leo P.
Rohm & Co., Ltd.
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