Semiconductor device downsizing its built-in driver

Details Semiconductor device downsizing its built-in driver Semiconductor device downsizing its built-in driver

2002-12-30

2004-06-29

Cuneo, Kamand (Department: 2829)

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

Of individual circuit component or element

C257S048000

Reexamination Certificate

active

06756803

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor package that mounts a plurality of semiconductor chips in combination, and merges them by installing wiring between the chips to exchange data, that is, to a semiconductor device assembled in a multi-chip package.
2. Description of Related Art
Recently, an increasing number of multi-chip packages (called “MCPs”from now on) have been used in electronic equipment such as mobile phones requiring miniaturization and versatility, as semiconductor products meeting demands of equipment manufacturers. The MCP consists of one package including combinations of LSIs such as logic and memory, digital and analog, and flash memory and SRAM LSIs, which are stacked and have wiring installed between the chips by wire bonding.
FIG. 13
is a block diagram showing a schematic internal configuration of a conventional multi-chip package including two-chips (semiconductor devices) combined together. In
FIG. 13
, the reference numeral
1100
designates an MCP, and reference numerals
1110
and
1120
each designate a chip constituting a semiconductor device mounted on the MCP
1100
. Although the two chips usually have different types of functions, it is not unlikely that they belong to the same type. In either case, they are assembled into the multi-chip structure to transfer data in one direction from one chip to the other, or to exchange data between them.
In the first chip
1110
, the reference numeral
500
designates an internal circuit, reference numerals
410
and
420
each designate an input buffer for the internal circuit
500
, and
430
and
440
each designate an output buffer. Reference numerals
101
-
104
designate pads that are formed on the chip, and are connected to the input terminals of the input buffers
410
and
420
and the output terminals of the output buffers
430
and
440
, respectively. Reference numerals
105
each designate a pad for one of other input/output terminals of the internal circuit
500
(not shown for the sake of simplicity). In the second chip
1120
, the reference numeral
501
designates an internal circuit,
411
designates an input buffer for the internal circuit
501
, and
441
designates an output buffer. The reference numeral
201
designates a pad formed on the chip
1120
to be connected to the input terminal of the input buffer
411
. Reference numerals
202
,
203
and
205
each designate a pad to be connected to one of the input/output terminals of the internal circuit
501
(not shown for the sake of simplicity) . Both the chips
1110
and
1120
have a configuration for exchanging data. Specifically, the pads
101
and
204
and the pads
104
and
201
are each interconnected by wires
701
and
702
. Thus, the output of the buffer
440
of the chip
1110
drives the chip
1120
via the pads
104
and
201
, and the output of the buffer
441
of the chip
1120
is supplied to the internal circuit
500
of the chip
1110
via the pads
204
and
101
. Reference numerals
601
-
606
designate external terminals of the MCP
1100
used for the chip
1110
, which are connected to the pads
102
,
103
and
105
via the wires
703
-
708
. Reference numerals
611
-
616
designate external terminals of the MCP
1100
used for the chip
1120
, which are connected to the pads
202
,
203
and
205
via wires
723
-
728
.
Generally, the pads, that is, the input/output terminals and output terminals of the semiconductor devices mounted on the MCP, fall into two types: the first type of pad is used for the external input/output terminals and output terminals after assembly (used in a state in which the MCP is installed into electronic equipment); and the second type of pad is used for the input and output only between the semiconductor devices assembled into the MCP.
As for the second type, Japanese patent application No. 2001-294539 applied by the assignee of the present invention discloses it. It discloses a configuration that controls the output driving power of the output buffer
440
by using a control signal
150
as shown in FIG.
13
.
FIG. 14
shows an example of the circuit configuration of the output buffer
440
.
In
FIG. 14
, the reference numeral
443
designates a normally used driver, and
444
designates a power adjusting driver. The output buffer
440
is supplied with a signal from the internal circuit
500
of
FIG. 13
as its input signal
160
, and its output appears at the output pad
104
. At a wafer test, the control signal
150
is placed at a “H” (high) level to enable the power adjusting driver
444
. Thus, the output buffer
440
can increase its driving power so that it can drive a large load capacitance of a tester. In addition, in the normally used state after the assembly, the power adjusting driver
444
is disabled by placing the control signal
150
at a “L” (low) level. Thus, the output buffer
440
can reduce its driving power after assembly, so that it drives only the another semiconductor device mounted on the MCP, that is, only the chip
1120
in the example of FIG.
13
. By thus switching the driving power in accordance with the usage condition, the output buffer
440
can drive the wiring between the chips in the MCP
1100
with smaller driving power in the normally used mode, thereby curbing the generation of drive noise affecting the operation, and limiting the increase in current consumption at the operation.
With the foregoing configuration, the conventional MCP has the following problems. First, consider the state in which the output buffer must drive only the another semiconductor device installed in the MCP after the assembly. In this case, the output buffer
440
carries out its driving through the normally used driver
443
only. In the course of this, the normally used driver
443
must always drive the drain capacitance of a P-channel transistor
446
and N-channel transistor
447
constituting the power adjusting driver
444
. In other words, even though the output buffer
440
is controlled such that its driving power is reduced to drive only the another semiconductor device, it must simultaneously drive with its small driving power the drain capacitance of the power adjusting driver
444
in the off state. Accordingly, the size of the normally used driver
443
must be determined considering the drain capacitance of the power adjusting driver
444
in the off state. This offers a problem of increasing the current consumption by that amount.
Second, as for the semiconductor devices to be installed in the MCP, and a structure provided for driving the another semiconductor device in the conventional technique to implement the MCP, the following problem arises. It is impossible for the output buffer
440
to restrict its size to a small one because the normally used driver
443
requires the driving power for driving the drain capacitance of the power adjusting driver
444
in the off state. For this reason, countermeasures against the noise generation and current consumption at the operation are limited, which hinders the optimization of the MCP product.
SUMMARY OF THE INVENTION
The present invention is implemented to solve the foregoing problems. It is therefore an object of the present invention to provide a semiconductor device that can supply the driving power required for a wafer test, and drive the another semiconductor device installed in the MCP while restricting the current consumption and preventing the drive noise adversely affecting the normal operation.
According to a first aspect of the present invention, there is provide a semiconductor device including: a first pad to be connected to another semiconductor device; a second pad for making a probing connection in a wafer test; a first buffer connected to the first pad for driving the another semiconductor device; and a second buffer driven by the first buffer, for driving a load capacitance of a tester connected to the second pad by driving power greater than that of the first buffer, the second buffer having its active/inactive st

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