Semiconductor devices

A semiconductor device has a constant-current circuit selectively operative in an operation mode among a writing mode in which a writing current for causing the antifuse to change in state from a breaking state to a conductive state is supplied to the antifuse, a sense mode in which a sensing current for detecting a state of the antifuse is supplied to the antifuse, and an additional writing mode in which an additional writing current for performing an additional writing is supplied to the antifuse which is subjected to writing.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a semiconductor device capable of 
implementing a desired circuit operation by writing a predetermined data 
into a finished product or finished goods which are referred to as a 
so-called PLD, FPGA and the like. 
2. Description of the Related Art 
Recently, there have been generally used programmable semiconductor devices 
referred to as programmable logic devices (PLDs), field programmable gate 
arrays (FPGAs) and the like. Such programmable semiconductor devices are 
suitable particularly for the use of small quantities and multi-variety, 
since writing programming data after completion of products thereinto 
enables a desired circuit wiring to be completed so as to implement a 
desired circuit operation. 
There are various schemes of implementing circuit wirings according to 
writing data in connection with such semiconductor devices. As one of such 
schemes, there is known a scheme in which fuses are provided in circuit 
wirings and a desired circuit wiring is implemented in accordance with a 
determination as to whether the fuse is melted to be disconnected. On the 
other hand, recently, there has been noticed a scheme in which a so-called 
antifuse is used instead of the fuse. The antifuse is an element to which 
an application of a voltage higher than the usual operating voltage allows 
the transition from the insulated state (hereinafter, referred to as 
"off-state") to the conductive state (hereinafter, referred to as 
"on-state") through the breakdown or the like. According to such 
antifuses, it is possible to produce elements within a semiconductor 
integrated circuit in an extremely small size such as the corresponding 
so-called via hole and the like. Thus, the antifuse has been noticed as an 
element which is suitable for a high integration much better than the 
fuse. 
With respect to schemes for writing of data into the antifuse, for example, 
Japanese Patent Laid Open Gazette Hei.3-225864 proposes one scheme. This 
proposed writing scheme is a constant-voltage writing scheme in which a 
predetermined voltage is applied between a word wire and a bit wire 
provided on a PROM so that an antifuse formed on a diffusion layer of the 
PROM is changed in condition from the off-state to the on-state. 
With respect to schemes for writing of data into the antifuse, European 
Patent Publication No. 0626726 also proposes one scheme. This data writing 
scheme is a scheme in which for each wire block provided with antifuses, a 
writing is carried out by applying a constant voltage to an antifuse 
within the block, thereafter it is determined as to whether the writing 
has been completed by causing a sense current to flow through the 
antifuse, and as a result, if it is determined that the writing has been 
completed, an additional writing is performed. 
Further, PCT/US92/06206, U.S. Pat. No. 5,243,226, and U.S. Pat. No. 
5,302,546 each disclose technology in which the constant-voltage writing 
scheme is adopted to precharge wire elements connected to antifuses to the 
intermediate potential before application of the writing voltage, and 
another technology in which after writing, a voltage is applied in a 
direction opposite to the direction of the voltage applied at the time of 
the writing so as to reduce the on-resistance of the antifuse which is 
changed in its state to be the on-state. Furthermore, Japanese Patent Laid 
Open Gazette Hei.6-506098, PCT/US92/01994, and U.S. Pat. No. 5,313,119 
each disclose technology in which the constant-voltage writing scheme is 
adopted, and a high writing voltage is applied to only the antifuses to be 
written, while the intermediate potential is applied to the remaining 
antifuses. 
With respect to constant-voltage writing schemes, other than the above, 
"Programming Antifuses in Crosspoint's FPGA" in proceedings of the IEEE 
1994 CUSTOM INTEGRATED CIRCUIT CONFERENCE 9.3 introduces a 
constant-voltage writing scheme proposed by the several FPGA makers 
(Actel, Quicklogic and Crosspoint). 
One of the problems of the constant-voltage writing scheme resides in the 
point that a constant voltage is applied to an antifuse to cause its state 
to be changed from the off-state to the on-state. Transition of the 
antifuse in state from the off-state to the on-state through a breakdown 
or the like causes the value of resistance of the antifuse to be reduced, 
so that the over-current flows for a relatively long time, for example, 
1-10 msec. Consequently, the overheat of the antifuses causes a large 
disunity in the value of resistance of the antifuse. Further, it happens 
that the overheat of the antifuses causes a melting to occur whereby the 
antifuses returning to the off-state. For example, according to the 
experiment by the applicants or inventors of the present application, in 
case of the constant-voltage writing scheme in which a current is clamped 
within a range of 0.1-20 mA, the value of resistance of the antifuses 
varies within a range of 40.OMEGA.-1 K.OMEGA.. This causes a large delay 
time and a large timing skew to be brought about. Thus, it is difficult to 
apply the constant-voltage writing scheme to a semiconductor device such 
as a PROM and a PLD for use in a high speed drive. 
In order to prevent a disunity in the turn-on resistance and an occurrence 
of the melting, it may be considered that the writing into the antifuses 
is implemented with a constant-current. While there is found no example in 
which a constant-current writing scheme is adopted for the antifuses, 
there is found an example, in connection with a programmable read only 
memory (PROM) which uses fuses as storage elements, in which a 
constant-current writing is performed on the fuses (cf. "NEC data book IC 
memory" 1989/1990, edited by NEC Corporation Semiconductor Application 
Technology Headquarters, issued by NEC Corporation Semiconductor Marketing 
Headquarters). 
According to the constant-current writing scheme as mentioned above, 
however, there is a need to attach a complicated control circuit such that 
a comparison voltage is produced from a constant-voltage supply, a flow 
current into fuses is converted into a voltage, the resultant voltage is 
compared with the comparison voltage to control the current in such a 
manner that the flow current is clamped not to exceed a predetermined 
value. According to such a constant-current writing scheme, it is obliged 
to perform a writing one bit by one bit thereby taking a lot of time for a 
writing, and in addition, in view of the fact that it is a specific 
writing scheme, there is a need to provide a dedicated PROM writer. If it 
is intended that the conventional scheme of writing into the fuses of the 
PROM is applied to a scheme of writing into the antifuses of the 
semiconductor device such as a PLD and the like as it is, there is a need 
to attach a complicated control circuit, and in addition, it is necessary 
for the semiconductor device to be provided with a writing-use 
constant-voltage supply terminal and a constant-current supply terminal as 
well. The number of constant-current supply terminals to be needed 
corresponds to the number of parallel writings. 
Even if there is adopted a scheme of performing a writing into antifuses 
with a constant-current, for example, such a simple scheme that a writing 
is performed with a predetermined time interval of constant-current pulse 
cannot yet avoid a large disunity in a value of the on-resistance. 
SUMMARY OF THE INVENTION 
In view of the foregoing, it is therefore an object of the present 
invention to provide a programmable semiconductor device having antifuses, 
which semiconductor device permits writing into the antifuses in such a 
manner that an on-resistance of the antifuse becomes a stably low value of 
resistance. 
To attain the above-mentioned object, according to the present invention, 
there is provided a first semiconductor device comprising a first signal 
line and a second signal line intersecting each other, and an antifuse 
located at an intersection point of the first signal line and a second 
signal line, wherein different circuit operations are implemented 
according as such a writing that an electric power is supplied to the 
antifuse in a breaking state so that the antifuse changes in a state to a 
settled conductive state is carried out or not on the antifuse located at 
the intersection point, said semiconductor device further comprising: 
a constant-current circuit for applying a voltage less than a predetermined 
voltage to the antifuse to supply a constant-current to the antifuse, said 
voltage being varied in accordance with a value of a resistance of the 
antifuse; and 
a detecting circuit for detecting whether a current starts to flow through 
the antifuse, 
wherein said constant-current circuit serves, before the lapse of a 
predetermined time after said detecting circuit detects the fact that the 
current starts to flow through the antifuse, to supply a predetermined 
first constant-current to the antifuse, and serves, after the lapse of the 
predetermined time, to stop supply of the current to the antifuse. 
Further, to attain the above-mentioned object, according to the present 
invention, there is provided a second semiconductor device comprising a 
first signal line and a second signal line intersecting each other, and an 
antifuse located at an intersection point of the first signal line and a 
second signal line, wherein different circuit operations are implemented 
according as such a writing that an electric power is supplied to the 
antifuse in a breaking state so that the antifuse changes in a state to a 
settled conductive state is carried out or not on the antifuse located at 
the intersection point, said semiconductor device further comprising: 
a constant-current circuit for applying a voltage less than a predetermined 
voltage to the antifuse to supply a constant-current to the antifuse, said 
voltage being varied in accordance with a value of a resistance of the 
antifuse; and 
a detecting circuit for detecting whether a current starts to flow through 
the antifuse, 
wherein said constant-current circuit serves, before the lapse of a 
predetermined time after said detecting circuit detects the fact that the 
current starts to flow through the antifuse, to supply a predetermined 
first constant-current to the antifuse, and serves, after the lapse of the 
predetermined time, to switch the predetermined first constant-current to 
a second constant-current smaller than the first constant-current so as to 
supply the second constant-current to the antifuse. 
Here, in the first semiconductor device or the second semiconductor device, 
it is preferable that said detecting circuit is a comparator for comparing 
a voltage appearing on one end of the antifuse or a voltage associated 
with the voltage on the one end of the antifuse with a predetermined 
reference voltage. 
Application of higher voltage than the usual operational voltage to an 
antifuse makes it possible to extrude a lot of metallic atoms (e.g. Al) of 
an electrode of the antifuse to a filament (a channel of a current formed 
by a breakdown), since a sectional area of the filament immediately after 
the breakdown of the antifuse is still small, and thus the current density 
is large (e.g. about 10.sup.9 A/cm.sup.2). It is estimated that the effect 
is proportional to power (the second power to the third power) of the 
current density (this is referred to "Electro Migration", and the current 
is referred to an EM current). A metal of the electrodes of both ends of 
the antifuse is melt by the heat generation due to the EM current, so that 
alloys are formed. However, when the EM current flows continuously for 
long time, stress remains on the filament owing to the overheat. This 
causes a resistance value of the antifuse to scatter largely. Thus, it may 
happen that melting occurs and this involves the off-state again. 
For these reasons, after the lapse of a predetermined time, it is switched 
to a constant-current (referred to an MT current) which is smaller than 
the EM current, or it is broken without the MT current flowing, whereby 
fusing for a metal of the electrodes is stably performed so that alloys 
are formed. On the other hand, even if a certain constant voltage is 
applied to the antifuse, a time from a starting point of the voltage 
application up to occurrence of the breakdown will be varied in accordance 
with antifuses. 
The first semiconductor device and the second semiconductor device 
according to the present invention have been made in view of the 
foregoing. According to those semiconductor devices, the constant-current 
circuit serves, before the lapse of a predetermined time after the 
detecting circuit detects the fact that the current starts to flow through 
the antifuse, to supply a predetermined first constant-current to the 
antifuse, and serves, after the lapse of the predetermined time, to stop 
supply of the current to the antifuse (the first semiconductor device). 
Alternatively, after the lapse of the predetermined time, it is to switch 
the predetermined first constant-current to a second constant-current 
smaller than the first constant-current so as to supply the second 
constant-current to the antifuse (the second semiconductor device). 
Consequently, the first constant-current causes a lot of metallic atoms of 
an electrode of the antifuse to be extruded to the filament, so that a 
small resistance value can be obtained. Further, the stop of supply of the 
current or switching of the predetermined first constant-current to a 
second constant-current smaller than the first constant-current, after the 
lapse of the predetermined time, makes it possible to prevent the 
over-heat, whereby fusing for a metal of the electrodes is stably 
performed so that alloys are formed. Therefore, it is possible to obtain 
the small resistance value, to reduce the disunity of the resistance 
value, and also to prevent the off-state again. 
Further, if there is used, as the detecting circuit, a comparator for 
comparing a voltage appearing on one end of the antifuse with a 
predetermined reference voltage, it is possible to simplify the circuit. 
Still further, according to the first semiconductor device and the second 
semiconductor device of the present invention, since the constant-current 
circuit is simplified in a structure, it is possible to incorporate the 
same into the chip, whereby a load of the external circuit and writing 
control circuit is reduced. In a case where the constant-current circuit 
is incorporated into the chip, since there is no need to prepare many 
external terminals for writing only, it is possible to effectively use the 
remaining terminals. Further, it is possible to simultaneously perform 
writing into a plurality of antifuses, thereby reducing writing time. 
To attain the above-mentioned object, according to the present invention, 
there is provided a third semiconductor device comprising a first signal 
line and a second signal line intersecting each other, and an antifuse 
located at an intersection point of the first signal line and a second 
signal line, wherein different circuit operations are implemented 
according as such a writing that an electric power is supplied to the 
antifuse in a breaking state so that the antifuse changes in a state to a 
settled conductive state is carried out or not on the antifuse located at 
the intersection point, said semiconductor device further comprising: 
a constant-current circuit selectively operative in an operation mode among 
a writing mode in which a writing current for causing the antifuse to 
change in state from a breaking state to a conductive state is supplied to 
the antifuse, a sense mode in which a sensing current for detecting a 
state of the antifuse is supplied to the antifuse, and an additional 
writing mode in which an additional writing current for performing an 
additional writing is supplied to the antifuse which is subjected to 
writing. 
According to the third semiconductor device of the present invention, the 
constant-current circuit is incorporated into the device, and in addition 
the constant-current circuit is operative selectively in the operational 
mode among the writing mode, the sense mode and the additional mode. These 
features permit the constant-current writing through supplying only a 
constant-voltage for writing from outside and then simply inputting 
address and data. Consequently, it is possible to perform the very easy 
writing when seeing from outside. 
Further, according to the third semiconductor device of the present 
invention, since writing is performed with the constant-current, and in 
addition, there is provided the additional writing mode, and the 
additional writing is also performed with the constant-current, it is 
possible to obtain the small resistance value, to reduce the disunity of 
the resistance value, and also to prevent the off-state again. 
Here, in the third semiconductor device of the present invention, it is 
preferable that said constant-current circuit has a voltage clamp circuit 
for limiting a voltage, which is applied to the antifuse in the breaking 
state, to such a level of voltage that said antifuse is kept on the 
breaking state. 
Adoption of the voltage clamp circuit makes it possible to prevent the 
antifuse, which is not to be changed in the state to the turn-on state 
when the constant-current circuit is operative in the sense mode, from 
unexpectedly changing in the state to the turn-on state. 
Further, in the third semiconductor device of the present invention, it is 
preferable that the semiconductor device further comprises a state 
detection circuit for detecting a state of the antifuse on the basis of a 
voltage which appears when the sensing current is supplied to the 
antifuse. 
Adoption of the state detection circuit makes it possible to detect the 
turn-on and turn-off states of the antifuse in the sense mode, and 
determine as to whether the rewriting is to be implemented or the 
additional writing is to be implemented. 
Furthermore, in the third semiconductor device of the present invention, it 
is preferable that said first signal line comprises a plurality of first 
signal lines mutually extending in parallel, and said second signal line 
comprises a plurality of second signal lines mutually extending in 
parallel, and said antifuse is arranged at each of intersection points of 
the plurality of first signal lines and the plurality of second signal 
lines, said semiconductor device further comprising: 
first switching circuits each connected in series to an associated one of 
said plurality of first signal lines; 
second switching circuits each connected in series to an associated one of 
said plurality of second signal lines; 
a first decoder for optionally selecting desired ones of said plurality of 
first signal lines through control of said first switching circuits; and 
a second decoder for optionally selecting desired ones of said plurality of 
second signal lines through control of said second switching circuits, 
wherein said constant-current circuit supplies constant-currents, which are 
controlled independently of each other on a parallel basis, are supplied 
to one or a plurality of antifuses which are simultaneously selected for 
writing in accordance with said first decoder and said second decoder in 
their combination. 
In the third semiconductor device of the present invention, the feature 
such that "said constant-current circuit supplies constant-currents, which 
are controlled independently of each other on a parallel basis, are 
supplied to one or a plurality of antifuses which are simultaneously 
selected for writing in accordance with said first decoder and said second 
decoder in their combination" makes it possible to perform the high speed 
writing. 
Further, in the third semiconductor device of the present invention, it is 
preferable that said first decoder and said second decoder have modes for 
simultaneously selecting all of the first signal lines and all of the 
second signal lines selected by said first decoder and said second 
decoder, respectively. 
In writing, when a voltage for supplying a writing current is applied, if a 
potential on a signal line to which said voltage is applied is different 
from a potential on a signal line involved in the antifuse, which is not 
intended to perform writing in conjunction with the former signal line, a 
voltage is instantaneously applied to the antifuse, and thus there is a 
fear such that the antifuse, which is not intended to perform writing, is 
inadvertently changed in the state to the turn-on state. For this reason, 
it is preferable that prior to writing, all of the first signal lines and 
all of the second signal lines are precharged beforehand to the potential, 
for example, one half of the writing voltage. In this case, if said first 
decoder and said second decoder have modes for simultaneously selecting 
all of the first signal lines and all of the second signal lines selected 
by said first decoder and said second decoder, respectively, then it is 
possible, prior to writing, to simultaneously precharge all of the first 
signal lines and all of the second signal lines, thereby reducing the set 
up time for the writing operation. 
Furthermore, in the third semiconductor device of the present invention, it 
is preferable that said constant-current circuit has: 
a reference current generating circuit for generating a reference current; 
and 
a constant-current supplying circuit for generating by the use of a current 
mirror circuit a constant-current according to the reference current 
generated from said reference current generating circuit, and supplying 
the constant-current thus generated to the antifuse. 
As mentioned above, if the constant-current circuit is constituted of the 
reference current generating circuit and the constant-current supplying 
circuit for generating by the use of a current mirror circuit a 
constant-current according to the reference current generated from said 
reference current generating circuit and supplying the constant-current 
thus generated to the antifuse, it is sufficient to generate a reference 
current once. Thereafter, the use of the current mirror circuit having a 
simple structure permits an easy copy of the reference current by the 
corresponding parallel writing number. Thus, it is possible to 
simultaneously supply to a plurality of antifuses constant-currents which 
are controlled independently of each other. 
It is possible to combine the first semiconductor device according to the 
present invention with the third semiconductor device according to the 
present invention. In connection with the semiconductor device according 
to the present invention in their combination, in the third semiconductor 
device according to the present invention, said semiconductor device 
further comprises a detecting circuit for detecting whether a current 
starts to flow through the antifuse in the writing mode, and 
wherein said constant-current circuit serves, in the writing mode, before 
the lapse of a predetermined time after said detecting circuit detects the 
fact that the current starts to flow through the antifuse, to supply a 
predetermined first constant-current to the antifuse, and serves, after 
the lapse of the predetermined time, to stop supply of the current to the 
antifuse. According to the invention as described above, it is possible to 
more stably change the antifuse in the state to the turn-on state of the 
low resistance. 
It is possible to combine the second semiconductor device according to the 
present invention with the third semiconductor device according to the 
present invention. In connection with the semiconductor device according 
to the present invention in their combination, in the third semiconductor 
device according to the present invention, said semiconductor device 
further comprises a detecting circuit for detecting whether a current 
starts to flow through the antifuse in the writing mode, and 
wherein said constant-current circuit serves, in the writing mode, before 
the lapse of a predetermined time after said detecting circuit detects the 
fact that the current starts to flow through the antifuse, to supply a 
predetermined first constant-current to the antifuse, and serves, after 
the lapse of the predetermined time, to switch the predetermined first 
constant-current to a second constant-current smaller than the first 
constant-current so as to supply the second constant-current to the 
antifuse. Also in this case, it is possible to more stably change the 
antifuse in the state to the turn-on state of the low resistance.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Hereinafter, there will be described embodiments of the present invention. 
FIG. 1 is a circuit diagram of an antifuse writing circuit of a PLD which 
incorporates thereinto a semiconductor device according to the first 
embodiment of the present invention. 
FIG. 1 shows an antifuse writing circuit comprises a constant-current 
circuit 100 for supplying a constant-current to antifuses 1, a detection 
circuit 200 for detecting whether or not a current starts to flow through 
the antifuses 1, and a block 300 in which a plurality of antifuses 1 are 
arranged and in addition circuits for optionally selecting the antifuses 1 
are disposed. 
The antifuses 1 of the block 300 are disposed at the crossing or 
intersection points of a plurality of first signal lines 2.sub.-- 1, 
2.sub.-- 2, . . . , 2.sub.-- m, which extend in a vertical direction, and 
a plurality of second signal lines 3.sub.-- 1, 3.sub.-- 2, . . . , 
3.sub.-- n, which extend in a horizontal direction. Connected to the first 
signal lines 2.sub.-- 1, 2.sub.-- 2, . . . , 2.sub.-- m and the second 
signal lines 3.sub.-- 1, 3.sub.-- 2, . . . , 3.sub.-- n are inputs and 
outputs of a plurality of circuits (not illustrated). These circuits will 
be each connected by wires which are different according as the associated 
antifuse 1 is kept on the off-state or is changed to the on-state. As a 
result, there will be implemented a resultant circuit which is different 
as a whole in accordance with writing data into the antifuses 1. 
In the block 300, the first signal lines 2.sub.-- 1, 2.sub.-- 2, . . . , 
2.sub.-- m are connected to first ends of the NMOS transistors 4.sub.-- 1, 
4.sub.-- 2, . . . , 4.sub.-- m, respectively. Second ends of the NMOS 
transistors 4.sub.-- 1, 4.sub.-- 2, . . . , 4.sub.-- m are connected to 
each other on a common basis, further connected to a non inverting input 
of a comparator 201, and connected via a PMOS transistor 106 to a writing 
power supply V.sub.PP (9V). The gates of the NMOS transistors 4.sub.-- 1, 
4.sub.-- 2, . . . , 4.sub.-- m are connected via voltage transformation 
type of inverters 6.sub.-- 1, 6.sub.-- 2, . . . , 6.sub.-- m, which will 
be described later, to the outputs of the NAND gates 7.sub.-- 1, 7.sub.-- 
2, . . . , 7.sub.-- m, respectively. 
First inputs of the NAND gates 7.sub.-- 1, 7.sub.-- 2, . . . , 7.sub.-- m 
are connected to the associated outputs of a column decoder 11, 
respectively. Inputted to the column decoder 11 are a column address for 
optionally selecting the first signal lines 2.sub.-- 1, 2 .sub.-- 2, . . . 
, 2.sub.-- m and a signal BLOCKO.sub.-- for enabling the column decoder 
11. 
Second inputs of the NAND gates 7.sub.-- 1, 7.sub.-- 2, . . . , 7.sub.-- m 
are connected to an output of a NAND gate 9 on a common connection basis. 
One input of the NAND gate 9 is connected to an output of a NAND gate 10. 
Another input of the NAND gate 9 is adapted to receive a read signal 
READ.sub.-- for checking as to whether or not the respective antifuses 1 
are properly in the off-state or the on-state after the completion of 
writing into the antifuses 1. Incidentally, there are not illustrated 
circuits (e.g. sense amplifiers and the like) for reading out. One of 
inputs of the NAND gate 10 is adapted to receive a program pulse signal 
PGM for performing writing into the antifuses 1. Another input of the NAND 
gate 10 is adapted to receive a writing data signal D for determining 
whether or not writing into the antifuses 1 is performed. 
The second signal lines 3.sub.-- 1, 3.sub.-- 2, . . . , 3.sub.-- n are 
connected to first ends of the NMOS transistors 5.sub.-- 1, 5.sub.-- 2, . 
. . , 5.sub.-- n, respectively. Second ends of the NMOS transistors 
5.sub.-- 1, 5.sub.-- 2, . . . , 5.sub.-- n are connected to the ground 
V.sub.SS on a common basis. The gates of the NMOS transistors 5.sub.-- 1, 
5.sub.-- 2, . . . , 5.sub.-- n are connected via voltage transformation 
type of inverters 8.sub.-- 1, 8.sub.-- 2, . . . , 8.sub.-- n to outputs of 
a row decoder 12, respectively. 
Inputted to the row decoder 12 are a row address for optionally selecting 
the second signal lines 3.sub.-- 1, 3.sub.-- 2, . . . , 3.sub.-- n and the 
signal BLOCKO.sub.-- for enabling the row decoder 12. 
One end of a PMOS transistor 101 of the constant-current circuit 100 is 
connected to the writing power supply V.sub.PP (9V). Another end of the 
PMOS transistor 101 is connected to a gate of the PMOS transistor 101, a 
gate of the PMOS transistor 106, and first ends of the resistances 102 and 
103. Another end of the resistance 102 is connected to an output of a 
voltage transformation type of inverter 104 to which a signal MT&EM, which 
is held in an "H" level during writing into the antifuses 1, is fed. On 
the other hand, another end of the resistance 103 is connected to the 
ground V.sub.SS through an NMOS transistor 105. A gate of the NMOS 
transistor 105 is connected to an output of a NOR gate 107. 
An inverting input of the comparator 201 of the detection circuit 200 
receives a comparison voltage (8V) to be compared with a voltage of a node 
CI associated with a voltage of one ends of the antifuses 1. An output of 
the comparator 201 is connected to one input of a NOR gate 203 via a delay 
circuit 202. Another input of the NOR gate 203 receives an inverted 
program pulse signal PGM.sub.-- of the above-mentioned program pulse 
signal PGM. An output of the NOR gate 203 is connected to one input of the 
NOR gate 107. Another input of the NOR gate 107 is adapted to receive a 
signal EM.sub.-- which is held in a "L" level during writing into the 
antifuses 1. 
FIGS. 2(A) and 2(B) are each a circuit diagram of a voltage transformation 
type of inverter by way of example. 
In these inverters, when an input of the inverter changes in level of an 
operational voltage V.sub.DD (e.g. 3.3V) of the circuit shown in FIG. 1 
from the "H" level to the "L" level, an output of the inverter changes in 
level of a writing voltage V.sub.PP (e.g. 9V) from the "L" level to the 
"HH" level, and reversely, when changing from the "L" level to the "H" 
level, changing from the "HH" level to the "L" level. Incidentally, here, 
while there are shown two examples of the inverter circuit, it is noted 
that the voltage transformation type of inverter is not restricted by 
these examples. 
FIG. 3 is a time chart useful for understanding an operation of the 
antifuse writing circuit. 
While the time chart does not show a read signal READ.sub.--, it is assumed 
that the read signal READ.sub.-- is set up to the "H" level when writing 
into the antifuses 1 is performed. 
First, the voltage transformation type of inverter 104 shown in FIG. 1 
receives the signal MT&EM having the level, and the NOR gate 107 receives 
the signal EM.sub.-- having the "L" level. While the program pulse signal 
PGM is outputted in the "L" level, the NAND gates 7.sub.-- 1, 7.sub.-- 2, 
. . . , 7.sub.-- m each receive the "L" level of signal via the NAND gate 
10 and the NAND gate 9. Hence, at that time, a designation of the 
antifuses 1 is not carried out. Since the NOR gate 203 receives the 
program pulse signal PGM.sub.-- having the "H" level, the NOR gate 203 
outputs a signal EMINH having the "L" level. The signal EMINH having the 
"L" level is fed to the NOR gate 107. Since the NOR gate 107 has received 
the signal EM.sub.-- having the "L" level, the NOR gate 107 outputs a 
signal having the "H" level whereby the NMOS transistor 105 turns on. 
Thus, a current (hereinafter referred to as MT current) flows into the 
voltage transformation type of inverter 104 through the writing power 
supply V.sub.PP, the PMOS transistor 101 and the resistance 102 in the 
named order. Further, a current flows into the ground V.sub.SS through the 
writing power supply V.sub.PP, the PMOS transistor 101, the resistance 103 
and the NMOS transistor 105 in the named order. The current, which flows 
through the PMOS transistor 101, is referred to as an EM current. At that 
time, while the PMOS transistor 106 also intends to conduct a current, the 
current does not flow through the PMOS transistor 106, because a 
designation of the antifuses 1 is not yet carried out and thus a current 
does not flow through the antifuses 1. Consequently, the potential of the 
node CI as the constant-current supply shown in FIG. 1 is the power supply 
voltage V.sub.PP (9V). The potential (9V) of the node CI is compared with 
the comparison voltage (8V) in the comparator 201. As a result, the 
comparator 201 outputs a signal having the "H" level, which signal is 
passed via the delay circuit 202 to the NOR gate 203. Since the NOR gate 
203 has received the program pulse signal PGM.sub.-- having the "H" level, 
the NOR gate 203 outputs the EMINH having the "L" level. 
Next, the column decoder 11 and the row decoder 12 receive the column 
address and the row address, respectively. These decoders 11 and 12 
further receive the enable signal BLOCKO.sub.-- having the "L" level. In 
case of writing into the antifuses 1 designated by the column address and 
the row address, the writing data D takes the "H" level. Even if any 
antifuse 1 is designated by the column address and the row address, the 
writing data D is kept on the "L" level when writing into the antifuse 1 
is not effected. Hereinafter, the explanation will be continued assuming 
that writing is effected on the designated antifuse 1. When the program 
pulse signal PGM changes in level to the "H" level, the column decoder 11 
outputs, at any associated output thereof according to the entered column 
address, the "H" level of signal, since the enable signal BLOCKO.sub.-- 
takes the "L" level. On the other hand, since both the program pulse 
signal PGM and the writing data D take the "H" level, a signal having the 
"H" level appears on the output of the NAND gate 9 via the NAND gate 10. 
Thus, any one of the NAND gates 7.sub.-- 1, 7.sub.-- 2, . . . , 7.sub.-- m 
outputs a signal having the "L" level, which signal is passed via the 
associated one of the voltage transformation type of inverters 6.sub.-- 1, 
6.sub.-- 2, . . . , 6.sub.-- m to the associated one of the NMOS 
transistors 4.sub.-- 1, 4.sub.-- 2, . . . , 4.sub.-- m, so that the 
associated NMOS transistor turns on. 
On the other hand, the row decoder 12 outputs, at any associated output 
thereof according to the entered row address, the "L" level of signal, 
since the enable signal BLOCKO.sub.-- takes the "L" level. Thus, the 
associated one of the NMOS transistors 5.sub.-- 1, 5.sub.-- 2, . . . , 
5.sub.-- n turns on via the associated one of the voltage transformation 
type of inverters 8.sub.-- 1, 8.sub.-- 2, . . . , 8.sub.-- n. In this 
manner, designated is the antifuse 1 located at the intersection point of 
the first signal lines 2.sub.-- 1, 2.sub.-- 2, . . . , 2.sub.-- m and the 
second signal lines 3.sub.-- 1, 3.sub.-- 2, . . . . , 3.sub.-- n. 
Incidentally, as noted above, if it is desired that the designated 
antifuse 1 is retained on the turn-off state, the writing data D is given 
with the "L" level. 
The PMOS transistor 101 and the PMOS transistor 106 constitutes a current 
mirror circuit. The gates of the PMOS transistors 101 and 106 are 
connected to each other. When the EM current (45 mA) flows through the 
PMOS transistor 101, the PMOS transistor 106 serves to supply the EM 
current (45 mA) to the antifuses 1. On the other hand, when the MT current 
(5 mA) flows through the PMOS transistor 101, the PMOS transistor 106 
serves to supply the MT current (5 mA) to the antifuses 1. 
The potential of the node CI is compared with the comparison voltage in the 
comparator 201. In the initial state in which the EM current is intended 
to flow into the designated antifuse 1, the resistance value of the 
antifuse 1 is still large and thus no current flows through the antifuse 
1. Consequently, the potential of the node CI is larger than the 
comparison voltage. As a result, even if the program pulse signal 
PGM.sub.--, which has been fed to the NOR gate 203, is of the "L" level, 
the signal EMINH is of the L" level, since the comparator 201 still 
outputs an "H" level of signal, which is passed via the delay circuit 202 
to the NOR gate 203. Thus, there is applied to the antifuse 1 a voltage 
which serves to cause the current (45 mA) corresponding to the EM current 
to flow through the antifuse 1. 
Next, it is assumed that after the lapse of a time QBD shown in FIG. 3, a 
breakdown occurs on the antifuse 1. At the time when the breakdown occurs, 
the resistance value of the antifuse 1 becomes rapidly small, so that a 
large current (about 45 mA) flows through the antifuse 1. As a result, the 
potential of the node CI goes down under 6V. Thus, the comparator 201 
outputs an "L" level of signal. 
The "L" level of signal is fed to the delay circuit 202 to be delayed by 
2.mu. sec. The delayed signal is fed to the NOR gate 203. Since the NOR 
gate 203 has received the program pulse signal PGM.sub.-- having the "L" 
level, the NOR gate 203 outputs the signal EMINH having the "H" level, 
which signal is passed via the NOR gate 107 to the NMOS transistor 105 to 
be turned off. As a result, the MT current (5 mA) flows through the 
antifuse 1. Thus, the potential of the node CI goes down under 0.5 V, so 
that the comparator 201 outputs in succession the "L" level of signal. In 
this manner, the EM current flows by a predetermined time (2.mu. sec.) 
after the breakdown occurs, and thereafter a switching is performed from 
the EM current (45 mA) to the MT current (5 mA) which is less than the EM 
current. Thus, it is possible to obtain a filament having a stable small 
resistance value, thereby preventing disunity in resistance value and 
off-state again due to the overheat. 
Next, after the lapse of a TPGM time since the program pulse signal PGM 
changed in level to the "H" level, when the program pulse signal PGM 
changes in level to the "L" level, the NAND gate 10 receives the "L" level 
of signal and thus outputs an "H" level of signal. As a result, the NAND 
gate 9 outputs an "L" level of signal, so that the designation of the 
antifuse 1 is released to break a current to the antifuse 1. Thus, the 
potential of the node CI goes up to about 9 V. The NOR gate 203 receives 
the "H" level of program pulse signal PGM.sub.-- and thus outputs the "L" 
level of signal EMINH, which is passed via the NOR gate 107 to the NMOS 
transistor 105. As a result, the NMOS transistor 105 turns on, so that the 
EM current flows through the PMOS transistor 101. 
Further after the lapse of a predetermined time, the column address, the 
row address and the writing data D are entered, and in addition the "H" 
level of program pulse signal PGM is entered. Then the above-mentioned 
operation is repeatedly carried out. Here, it is noted that as shown in 
FIG. 3, even if the respective antifuses 1 are different in the breakdown 
time from each other, writing into the antifuses 1 is performed in 
compliance with the different breakdown time, thereby obtaining filaments 
each having uniformly stable resistance value. 
Incidentally, according to the present embodiment, the constant-current 
circuit 100 and the detection circuit 200, which correspond to the writing 
circuit referred to in the present invention, are mounted together with 
the block 300 on one chip. While it is preferable that those elements are 
mounted on one chip, the writing circuit referred to in the present 
invention is not restricted to one mounted on the chip. It is acceptable 
to adopt one which is adapted to attach when writing. 
FIG. 4 is a circuit diagram of a writing circuit portion into antifuses of 
a semiconductor device according to the second embodiment of the present 
invention; 
The writing circuit portion shown in FIG. 4 comprises: a reference current 
generating circuit 400 for generating reference currents according to a 
writing mode, a sense mode and a additional writing mode; a comparison 
voltage generating circuit 500 for generating a comparison voltage at the 
time of the sense mode; a plurality of blocks 600.sub.-- 1, 600.sub.-- 2, 
. . . , 600.sub.-- k in each of which a plurality of antifuses are 
arranged; a determination gate circuit 700 for outputting a determination 
result as to whether the proper writing is carried out at the time of the 
sense mode; and a precharge control circuit 800 for transmitting a control 
signal when a precharge is performed. 
Here, it is noted that the writing mode implies a mode in which a writing 
current flows through antifuses 31 in the off state to cause a transition 
of the antifuses 31 into the on state; the sense mode implies a mode in 
which a sense current flows through the antifuses 31 to sense whether a 
proper writing into the antifuses 31 has been carried out; and the 
additional writing mode implies a mode in which an additional current 
flows through the antifuses 31, which has been subjected to the transition 
into the on state, to ensure the on state of the antifuses 31. 
Incidentally, it may happen that the term "writing" is used as the general 
term for a series of operation of writing in combination of the writing 
mode, the sense mode and the additional writing mode. 
Circuits of the blocks 600.sub.-- 1, 600.sub.-- 2, . . . , 600.sub.-- k are 
the same as each other. Hence, only the block 600.sub.-- 1 is illustrated, 
and will be explained hereinafter. 
The antifuses 31 of the block 600 are disposed at the crossing or 
intersection points of a plurality of first signal lines 32.sub.-- 
1.sub.-- 1, 32.sub.-- 1.sub.-- 2, . . . , 32.sub.-- 1.sub.-- m, which 
extend in a vertical direction, and a plurality of second signal lines 
33.sub.-- 1.sub.-- 1, 33.sub.-- 1.sub.-- 2, . . . , 33.sub.-- 1.sub.-- n, 
which extend in a horizontal direction. Connected to the first signal 
lines 32.sub.-- 1.sub.-- 1, 32.sub.-- 1.sub.-- 2, . . . , 32.sub.-- 
1.sub.-- m and the second signal lines 33.sub.-- 1.sub.-- 1, 33.sub.-- 
1.sub.-- 2, . . . , 33.sub.-- 1.sub.-- n are inputs and outputs of a 
plurality of circuits (not illustrated). These circuits will be each 
connected by wires which are different according as the associated 
antifuse 31 is kept on the off-state or is changed to the on-state. As a 
result, there will be implemented a resultant circuit which is different 
as a whole in accordance with writing data into the antifuses 31. 
In the block 600.sub.-- 1, the first signal lines 32.sub.-- 1.sub.-- 1, 
32.sub.-- 1.sub.-- 2, . . . , 32.sub.-- 1.sub.-- m, are connected to one 
ends of PMOS transistors 34.sub.-- 1.sub.-- 1, 34.sub.-- 1.sub.-- 2, . . . 
, 34.sub.-- 1.sub.-- m, respectively. Another ends of the PMOS transistors 
34.sub.-- 1.sub.-- 1, 34.sub.-- 1.sub.-- 2, . . . , 34.sub.-- 1.sub.-- m 
are connected to each other on a common basis, and connected via a 
constant-current supply line 36 and a PMOS transistor 37 to a writing 
power supply V.sub.PP. The gates of the PMOS transistors 34.sub.-- 1.sub. 
1, 34.sub.-- 1.sub.-- 2, . . . , 34.sub.-- 1.sub.-- m are connected to a 
column decoder (cf. FIG. 5(A)) which will be described later. The gate of 
the PMOS transistor 37 is connected to a constant-current level 
transmission line 40 extending from the reference current generating 
circuit 400 crossing the blocks 600.sub.-- 1, 600.sub.-- 2, . . . , 
600.sub.-- k. 
The second signal lines 33.sub.-- 1.sub.-- 1, 31.sub.-- 2.sub.--, . . . , 
33.sub.-- 1.sub.-- n are connected to one ends of NMOS transistors 
35.sub.-- 1.sub.-- 1, 35.sub.-- 1.sub.-- 2, . . . , 35.sub.-- 1.sub.-- n, 
respectively. Another ends of the NMOS transistors 35.sub.-- 1.sub.-- 1, 
35.sub.-- 1.sub.-- 2, . . . , 35.sub.-- 1.sub.-- n are connected via the 
NMOS transistor 38 to the ground V.sub.SS on a common basis, and further 
connected via the PMOS transistor 39 to the constant-current supply line 
36. The gates of the NMOS transistors 35.sub.-- 1.sub.-- 1, 35.sub.-- 
1.sub.-- 2, . . . , 35.sub.-- 1.sub.-- n are connected to a row decoder 
(cf. FIG. 5(B)) which will be described later. The gates of the NMOS 
transistor 38 and the PMOS transistor 39 are connected to a first 
precharge control line 802 extending from an output of a voltage 
transformation type of inverter 801 of the precharge control circuit 800 
crossing the blocks 600.sub.-- 1, 600.sub.-- 2, . . . , 600.sub.-- k. The 
voltage transformation type of inverter 801 receives a precharge control 
signal PRCG. 
In the comparison voltage generating circuit 500, a resistor 501, a 
resistor 502 and an NMOS transistor 503 are connected in series between 
the writing power supply V.sub.PP and the ground V.sub.SS. The NMOS 
transistor 503 is controlled in its turn on and off in accordance with the 
sense signal SENSE. 
A first comparison signal line 504 extends from the connecting point of the 
resistors 501 and 502 crossing the blocks 600.sub.-- 1, 600.sub.-- 2, . . 
. , 600.sub.-- k. A first comparison voltage VSND is transferred on the 
first comparison signal line 504 when the sense signal SENSE is of the "H" 
level. Here, the resistor 501 and the resistor 502 are the same as each 
other in their resistance value. Consequently, the first comparison 
voltage VSND is approximately V.sub.PP /2. The NMOS transistor 503 is 
provided for the purpose of preventing unnecessary power consumption, and 
is operative to turn on in the sense mode. 
Further, in the comparison voltage generating circuit 500, an NMOS 
transistor 505, a resistor 506, a resistor 507 and an NMOS transistor 508 
are connected in series between the writing power supply V.sub.PP and the 
ground V.sub.SS. A gate of the NMOS transistor 505 is connected to the 
first comparison signal line 504. The NMOS transistor 508 is controlled in 
its turn on and off in accordance with the sense signal SENSE. 
A second comparison signal line 509 extends from the connecting point of 
the resisters 506 and 507 crossing the blocks 600.sub.-- 1, 600.sub.-- 2, 
. . . , 600.sub.-- k. A second comparison voltage VSON is transferred on 
the second comparison signal line 509 when the sense signal SENSE is of 
the "H" level. The second comparison voltage VSON is set up to a voltage 
higher than that appearing on the constant-current supply line 36 when the 
sense current flows through the antifuse 31 after transition into the 
turn-on state, that is, 
EQU VSON&gt;(ON-resistance of the antifuse 31).times.sense current 
Here, the NMOS transistor 505 is of a source follower, and the second 
comparison voltage VSON is defined by a voltage which will be derived when 
a voltage, which is lower by a threshold voltage V.sub.TN of the NMOS 
transistor than the first comparison voltage VSND, is resistance-divided 
by the resistor 506 (resistance value R.sub.506) and the resistor 507 
(resistance value R.sub.507), that is, 
EQU VSON=(VSND-V.sub.TN).multidot.R.sub.507 /(R.sub.506 +R.sub.507) 
The NMOS transistor 508 is provided for the purpose of preventing 
unnecessary power consumption, and is operative to turn on in the sense 
mode which needs the comparison voltage. 
In the reference current generating circuit 400, there is provided a PMOS 
transistor 401. A gate of the PMOS transistor 401 is connected to a 
constant-current level transmission line 40. Hence, the PMOS transistor 
401 and the PMOS transistor 37 of the block 600.sub.-- 1 constitutes a 
current mirror circuit. When a reference current I.sub.SN flows through 
the PMOS transistor 401, the constant-current corresponding to the 
reference current I.sub.SN is supplied to the antifuse 31 side via the 
PMOS transistor 37 of the block 600.sub.-- 1. 
Connected to the PMOS transistor 401 are three resistors 402, 403 and 404. 
Another end of the resistor 402 is connected to an output of a voltage 
transformation type of inverter 405. Another ends of the resistors 403 and 
404 are connected to the ground V.sub.SS via NMOS transistors 406 and 407, 
respectively. 
As the resistors 402, 403 and 404, and the resistors 501, 502, 506 and 507 
in the comparison voltage generating circuit 500, a polysilicon 
resistance, a well resistance, a diffusion resistance and FET resistance 
may be used. 
The voltage transformation type of inverter 405 receives in anyone of the 
writing mode, the sense mode and the additional writing mode an "H" level 
of pulse signal S/P/A. In a mode other than those modes, that is, the 
usual operation mode in which writing into the antifuses 31 is terminated 
and the semiconductor device performs a predetermined circuit operation, 
an input of the voltage transformation type of inverter 405 is kept on an 
"L" level. 
A gate of the NMOS transistor 406 receives a program signal PROG. The 
program signal PROG is a pulse signal which takes an "H" level while the 
writing into the antifuse 31 is being performed and also while the 
additional writing bring performed. 
A gate of the NMOS transistor 407 receives an additional writing signal 
ADDP. The additional writing signal ADDP is a pulse signal which takes an 
"H" level only while the additional writing into the antifuse 31 is being 
performed. 
In this manner, in the sense mode, the "H" level of signal S/P/A appears, 
so that the reference current I.sub.SN, for example, 3 mA, flows through 
the PMOS transistor 401; in the writing mode, both the pulse signal S/P/A 
and the program signal PROG appear in the form of the "H" level, so that 
the reference current I.sub.SN, for example, 10 mA, flows through the PMOS 
transistor 401; and in the additional writing mode, the signal S/P/A, the 
program signal PROG and in addition the additional writing signal ADDP 
appear in the form of the "H" level, so that the reference current 
I.sub.SN, for example, 20 mA, flows through the PMOS transistor 401. 
In the sense mode, the voltage transformation type of inverter 405 receives 
the pulse signal S/P/A, while the gates of the NMOS transistors 503 and 
508 of the comparison voltage generating circuit 500 receive the sense 
signal SENSE. Thus, the reference current for sensing flows through the 
reference current generating circuit 400, so that the sense current flows 
through the constant-current supply line 36 via the PMOS transistor 37. 
The comparison voltage generating circuit 500 generates two comparison 
voltages VSND and VSON, which are passed to the comparators 41 and 42, 
respectively. A PMOS transistor 43 for voltage clamping is disposed 
between the constant-current supply line 36 and the ground V.sub.SS. A 
gate of the PMOS transistor 43 receives the comparison voltage VSND. 
Consequently, in the sense mode, the maximum voltage applied to the 
antifuses 31 via the constant-current supply line 36 is clamped, when the 
threshold voltage of the PMOS transistor 43 is expressed by V.sub.TP, to 
VSND+V.sub.TP. This voltage is set up to such a voltage level that even if 
this voltage is applied to the antifuse 31 in the turn-off state, the 
antifuse 31 in the turn-off state does not change in the state to the 
turn-on state. This is a measure for preventing the antifuse 31 in the 
turn-off state from unexpectedly changing in state to the turn-on state in 
the sense mode in which it is determined whether the antifuse 31 is in the 
turn-on state or the turn-off state. When the sense current is supplied to 
the antifuse 31 in the turn-on state, the voltage appearing on the 
constant-current supply line 36 will be remarkably lower voltage than the 
clamp voltage. 
Another terminals of the comparators 41 and 42, which are different from 
the one terminals to which the comparison voltages VSND and VSON are 
respectively applied, are connected to the constant-current supply line 
36. 
An output of the comparator 41 is fed to a NAND gate 44, and an output of 
the comparator 42 is fed to a OR gate 45. The NAND gate 44 and the OR gate 
45 receive an expected value PDATA ("L" level in the turn-on state) in the 
turn-on state and turn-off state of the antifuse 31 now sensed. An output 
of the NAND gate 44 and an output of the OR gate 45 are fed to a NAND gate 
46. An output of the NAND gate 46 is fed to a NAND gate 701 of a 
determination gate circuit 700. In a similar fashion, with respect to the 
respective NAND gates 46 on the whole blocks 600.sub.-- 1, 600.sub.-- 2, . 
. . , 600.sub.-- k, outputs of those NAND gates 46 are fed to the NAND 
gate 701 of the determination gate circuit 700. 
In a case where the antifuse 31 of interest, to which the sense current is 
intended to be supplied, is in the turn-off state, the potential of the 
constant-current supply line 36 becomes the clamp voltage and then it is 
higher than the comparison voltage VSND. Hence, the output of the 
comparator 41 takes an "H" level. When it matches with the expected value 
PDATA, the NAND gate 44 outputs an "L" level of signal, and thus the NAND 
gate 46 outputs an "H" level of signal. 
On the other hand, when the antifuse 31, to which the sense current is 
supplied, is in the turn-on state, the potential of the constant-current 
supply line 36 becomes a voltage which is lower than the comparison 
voltage VSON. Hence, the output of the comparator 42 takes an "L" level. 
When it matches with the expected value PDATA, the OR gate 45 outputs an 
"L" level of signal, and the NAND gate 46 outputs an "H" level of signal. 
When the sense current flows through the antifuse 31, if the potential of 
the constant-current supply line 36 is lower than the comparison voltage 
VSND and is higher than the comparison voltage VSON, the NAND gate 46 
outputs an "L" level of signal. 
When the NAND gate 46 outputs an "H" level of signal, it indicates that the 
turn-on or turn-off state of the antifuse 31 now sensed in the block 
600.sub.-- 1 is normal. On the other hand, when the NAND gate 46 outputs 
an "L" level of signal, it indicates that the antifuse 31 is of failure or 
is incomplete in writing. 
With respect to the respective NAND gates 46 on the whole blocks 600.sub.-- 
1, 600.sub.-- 2, . . . , 600.sub.-- k, if those NAND gates 46 output "H" 
level of signals, the NAND gate 701 outputs an "L" level of output signal 
PASS.sub.-- which indicates that all of the antifuses of each of the 
blocks 600.sub.-- 1, 600.sub.-- 2, . . . , 600.sub.-- k are normal. 
FIGS. 5(A) and 5(B) are diagrams showing input and output signals of a 
column decoder and a row decoder, respectively. 
The column decoder 50.sub.-- 1 and the row decoder 60.sub.-- 1 shown in 
FIGS. 5(A) and 5(B) correspond to the block 600.sub.-- 1 shown in FIG. 4. 
The same column decoder and the row decoder as the column decoder 
50.sub.-- 1 and the row decoder 60.sub.-- 1 are provided for each of the 
blocks 600.sub.-- 1, 600.sub.-- 2, . . . , 600.sub.-- k shown in FIG. 4. 
Regarding the column decoder 50.sub.-- 1, when an enable signal CSEL.sub.-- 
appears with an "H" level, all output signals COL11.sub.--, COL12.sub.--, 
. . . , COL1m.sub.-- appear with an "H" level, so that all the PMOS 
transistors 34.sub.-- 1.sub.-- 1, 34.sub.-- 1.sub.-- 2, . . . , 34.sub.-- 
1.sub.-- m, as shown in FIG. 4, turn off. When the enable signal 
CSEL.sub.-- appears with an "L" level and a signal CALL appears with an 
"L" level, anyone of the output signals COL11.sub.--, COL12.sub.--, . . . 
, COL1m.sub.-- appears with an "L" level in accordance with the entered 
column address CADDR, so that anyone of the PMOS transistors 34.sub.-- 
1.sub.-- 1, 34.sub.-- 1.sub.-- 2, . . . , 34.sub.-- 1.sub.-- m, as shown 
in FIG. 4, turns on. When the enable signal CSEL.sub.-- appears with an 
"L" level and the signal CALL appears with an "H" level, all of the output 
signals COL11.sub.--, COL12.sub.--, . . . , COL1m.sub.-- appears with an 
"L" level, so that all the PMOS transistors 34.sub.-- 1.sub.-- 1, 
34.sub.-- 1.sub.-- 2, . . . , 34.sub.-- 1.sub.-- m, as shown in FIG. 4, 
turn on. 
Regarding the row decoder 60.sub.-- 1, when an enable signal RSEL.sub.-- 
appears with an "H" level, all output signals ROW11.sub.--, ROW12.sub.--, 
. . . , ROW1n.sub.-- appear with an "L" level, so that all the NMOS 
transistors 35.sub.-- 1.sub.-- 1, 35.sub.-- 1.sub.-- 2, . . . , 35.sub.-- 
1.sub.-- n, as shown in FIG. 4, turn off. When the enable signal 
RSEL.sub.-- appears with an "L" level and a signal RALL appears with an 
"L" level, anyone of the output signals ROW11.sub.--, ROW12.sub.--, . . . 
, ROW1m.sub.-- appears with an "H" level in accordance with the entered 
row address RADDR, so that anyone of the NMOS transistors 35.sub.-- 
1.sub.-- 1, 35.sub.-- 1.sub.-- 2, . . . , 35.sub.-- 1.sub.-- n, as shown 
in FIG. 4, turns on. When the enable signal RSEL.sub.-- appears with an 
"L" level and the signal RALL appears with an "H" level, all of the output 
signals ROW11.sub.--, ROW12.sub.--, . . . , ROW1n.sub.-- appears with an 
"H" level, so that all the RMOS transistors 35.sub.-- 1.sub.-- 1, 
35.sub.-- 1.sub.-- 2, . . . , 35.sub.-- 1.sub.-- n, as shown in FIG. 4, 
turn on. 
When writing of the antifuses 31 is performed, first, prior to writing, the 
CALL signal and the RALL signal are given with "H" level; all of the PMOS 
transistors 34.sub.-- 1.sub.-- 1, 34.sub.-- 1.sub.-- 2, . . . , 34.sub.-- 
1.sub.-- m, as shown in FIG. 4, and all the NMOS transistors 35.sub.-- 
1.sub.-- 1, 35.sub.-- 1.sub.-- 2, . . . , 35.sub.-- 1.sub.-- n, as shown 
in FIG. 4, are turned on; and the PRCG signal is given with the "H" level. 
Thereafter, the S/P/A signal and the SENSE signal are given with an "H" 
level. Thus, the current, which is the same as the sense current in the 
level, flows through all the plurality of first signal lines 32.sub.-- 
1.sub.-- 1, 32.sub.-- 1.sub.-- 2, . . . , 32.sub.-- 1.sub.-- m, and all 
the plurality of second signal lines 33.sub.-- 1.sub.-- 1, 33.sub.-- 
1.sub.-- 2, . . . , 33.sub.-- 1.sub.-- n, so that all those first and 
second signal lines are precharged to the same voltage, that is, 
VSND+V.sub.TP. After the termination of the precharge, the CSEL.sub.-- 
signal and the RSEL.sub.-- signal are given with an "H" level, and the 
PRCG signal returns in level to an "L" level. Then, writing of the 
antifuses 31 is performed. 
The precharge on the first and second signal lines prior to the writing, as 
mentioned above, inhibits the over voltage from being applied to other 
than the antifuses into which writing is intended, thereby preventing 
unexpected writing into those antifuses from being carried out. 
FIG. 6 is a time chart showing a relationship among the S/P/A signal, the 
PROG signal, the ADDP signal and the SENSE signal when a writing into 
antifuses is performed. 
First, signals are outputted from the column decoder 50.sub.-- 1 and the 
row decoder 60.sub.-- 1 in such a manner that one of m pieces of the PMOS 
transistors 34.sub.-- 1.sub.-- 1, 34.sub.-- 1.sub.-- 2, . . . , 34.sub.-- 
1.sub.-- m and one of n pieces of the NMOS transistors 35.sub.-- 1.sub.-- 
1, 35.sub.-- 1.sub.-- 2, . . . , 35.sub.-- 1.sub.-- n turn on, so that the 
antifuse 31 at the their crossing point is designated. 
Incidentally, when the antifuse 31 at the their crossing point is kept on 
the turn-off state, at least one of the CSEL.sub.-- signal and the 
RSEL.sub.-- signal, which are fed to the column decoder 50.sub.-- 1 and 
the row decoder 60.sub.-- 1, respectively, is given with an "H" level. In 
this manner, all of the PMOS transistors 34.sub.-- 1.sub.-- 1, 34.sub.-- 
1.sub.-- 2, . . . , 34.sub.-- 1.sub.-- m or all of the NMOS transistors 
35.sub.-- 1.sub.-- 1, 35.sub.-- 1.sub.-- 2, . . . , 35.sub.-- 1.sub.-- n 
turn off, so that writing into the antifuse 31 to be designated by the 
column address CADDR and the row address RADDR is not implemented. 
An operation of the antifuse designation is performed in parallel with 
respect to the respective blocks 600.sub.-- 1, 600.sub.-- 2, . . . , 
600.sub.-- k. 
Here, it is assumed that the antifuse 31 on a certain crossing point in the 
block 600.sub.-- 1 is designated for writing into the antifuse 31. 
Next, as shown in FIG. 6, the S/P/A signal and the PROG signal are given 
with the pulse shaped "H" level (pulse a in FIG. 6). These signals cause 
writing for the first time to be carried out. Subsequently, the S/P/A 
signal and the SENSE signal are given with the pulse shaped "H" level 
(pulse b in FIG. 6). These signals serve to determine as to whether or not 
the antifuse of interest to be written changes in state to the turn-on 
state. If the antifuse of interest is still in the turn-off state, again 
the S/P/A signal and the PROG signal are given with the pulse shaped "H" 
level (pulse c in FIG. 6), so that rewriting operation is carried out. 
Next, the S/P/A signal and the SENSE signal are given with the pulse 
shaped "H" level (pulse d in FIG. 6) to determine as to whether or not the 
antifuse of interest changes in state to the turn-on state. This routine 
is repeatedly carried out in case of need. According to the timing of 
pulse x, when all of the blocks 600.sub.-- 1, 600.sub.-- 2, . . . , 
600.sub.-- k are in the states as indicated by the expected value PDATA, 
the PASS.sub.-- signal is given with an "L" level, so that it is detected 
that the normal writing has been performed. Then, the S/P/A signal, the 
PROG signal and the ADDP signal are given with the "H" level by the same 
time interval as the total pulse width of the previous writing pulses a 
and c, so that the additional writing is performed by the same time as the 
total of times required for writing. This causes the antifuse subjected to 
writing to be surely in the turn-on state. 
The above-mentioned routine is repeatedly performed while sequentially 
altering the addresses CADDR and RADDR which are applied to the column 
decoder 50.sub.-- 1 and the row decoder 60.sub.-- 1, respectively. 
Incidentally, from the terminal for supplying the writing power supply 
voltage V.sub.PP, the writing power supply voltage V.sub.PP, for example, 
10V, is supplied while the above-mentioned writing is carried out; in a 
non-writing test mode, which will be described latter, the middle order of 
voltage (e.g. 6.5V), which does not cause the antifuse in the turn-off 
state to change in state to the turn-on state, is supplied; and in a usual 
operation mode, the logic voltage (e.g. 3.3V) of the internal circuit is 
supplied. 
The non-writing test mode implies a mode for implementing a test for 
detecting the process failure of the antifuses, and specifically, a 
non-writing test for confirming that even if the above-mentioned middle 
order of voltage (e.g. 6.5V) is applied to all of the antifuses, all the 
antifuses are kept on the turn-off state. Such a non-writing test mode is 
adopted for determination of quality of the goods or products. In this 
case, "H" level of CALL signal and RALL signal are applied to the column 
decoder 50.sub.-- 1 and the row decoder 60.sub.-- 1, respectively, so that 
all of the PMOS transistors 34.sub.-- 1.sub.-- 1, 34.sub.-- 1.sub.-- 2, . 
. . , 34.sub.-- 1.sub.-- m or all of the NMOS transistors 35.sub.-- 
1.sub.-- 1, 35.sub.-- 1.sub.-- 2, . . . , 35.sub.-- 1.sub.-- n are turned 
on. However, different from the case of the precharge, the PROG signal is 
kept on the "L" level, and in addition, the side in which the NMOS 
transistors 35.sub.-- 1.sub.-- 1, 35.sub.-- 1.sub.-- 2, . . . , 35.sub.-- 
1.sub.-- n are connected on a common basis is connected to the ground 
V.sub.SS. In this condition, the writing current is supplied, while the 
writing power supply voltage V.sub.PP is the middle order of voltage (e.g. 
6.5V). When all the antifuses are kept on the turn-off state, the middle 
order of voltage appears on the constant-current supply line 36. When 
there occurs such a failure that anyone of the antifuses becomes the 
turn-on state, a remarkably lower voltage than the middle order of voltage 
appears on the constant-current supply line 36. The presence or absence of 
the failure antifuses can be detected by sensing through setting the 
expected value PDATA with an "H" level and the SENSE signal with an "H" 
level. 
Next, there will be explained the modification of the second embodiment as 
mentioned above. 
First, with respect to the reference current generating circuit 400, 
according to the second embodiment, in the writing mode, the sense mode 
and the additional writing mode, the mutually different reference currents 
I.sub.SN are produced. However, it is acceptable to modify the reference 
current generating circuit 400 in such a manner that in the additional 
writing mode the current value is selected to be the same as that in the 
writing mode, and the pulse width is extended thereby performing the 
additional writing. Specifically, the current value is given with, for 
example, 10 mA rather than 20 mA, and instead the pulse width for the 
additional writing is extended twice. In this case, it is possible to omit 
the resister 404 and the NMOS transistors 407 shown in FIG. 4. 
Further, it is acceptable that the reference current in the writing mode 
and the reference current in the sense mode are the same as each other. In 
this case, it is possible to omit the resister 403 and the NMOS transistor 
406. Distinction between the writing mode and the sense mode is made, 
according as the voltage clamp is effected through providing an "H" level 
for the sense signal (sense mode), and depending on the pulse width. 
With respect to the comparison voltage generating circuit 500, it is 
acceptable to replace the resisters 501 and 502 with FETs. In this case, 
it is possible to unify the resister 502 and the NMOS transistor 503. FIG. 
7 is a circuit diagram of a comparison voltage generating circuit for 
generating the comparison voltage VSND, which circuit is arranged in the 
manner as mentioned above. 
Likely, it is acceptable to replace the resisters 506 and 507 with FETs. In 
this case, it is possible to unify the resister 507 and the NMOS 
transistor 508. FIG. 8 is a circuit diagram of a comparison voltage 
generating circuit for generating the comparison voltage VSON, which 
circuit is arranged in the manner as mentioned above. 
According to the circuit shown in FIG. 4, the reference current at the time 
of the sense mode is generated in the reference current generating circuit 
400 by means of providing the S/P/A signal having an "H" level, so that 
the same level of current is generated in the current mirror circuit. 
However, it is acceptable that as shown in FIG. 9, a sense current is 
supplied from the comparison voltage VSND via the NMOS transistor 505 and 
the resister 510 to the constant-current supply line 36. In this case, in 
a case where the antifuses are in the turn-off state, there appears a 
voltage which is lower by the corresponding threshold voltage V.sub.TN of 
the NMOS transistor 505 than the comparison voltage VSND, and thus there 
is no need to provide the clamp circuit with the PMOS transistor 43 as 
shown in FIG. 4. However, in this case, a voltage VSOFF, which is lower by 
the corresponding threshold voltage V.sub.TN of the NMOS transistor 511 
than the resultant voltage, is supplied to the comparator 41 as a 
comparison voltage. 
FIG. 10 is a circuit diagram of a writing circuit portion into antifuses of 
a semiconductor device according to the third embodiment of the present 
invention. In FIG. 10, the same parts are denoted by the same reference 
numbers as those of FIG. 4. And the redundant explanation will be omitted. 
According to the circuit shown in FIG. 10, as compared with the circuit 
shown in FIG. 4, the comparison voltage generating circuit 500 is provided 
with a breakdown detecting comparison voltage generating circuit 520. 
Further, there are added a delay circuit 48 connected to an output of the 
comparator 42, and an AND gate 49 of which inputs receive an output signal 
of the comparator 42 and the program signal PROG, and of which an output 
is connected to the gate of the NMOS transistor 406. 
The reference current generating circuit 400 is provided for each of the 
blocks 600.sub.-- 1, 600.sub.-- 2, . . . , 600.sub.-- k. 
The breakdown detecting comparison voltage generating circuit 520 is a 
circuit for generating a comparison voltage to detect whether the antifuse 
31 occurs a breakdown in the writing mode, wherein a resister 512 and an 
NMOS transistor 513 are connected in series between the second comparison 
signal line 509 and the ground V.sub.SS. A gate of the NMOS transistor 513 
receives the program signal PROG. 
In the writing mode, the program signal PROG appears in an "H" level and 
the sense signal SENSE appears in an "L" level. Consequently, there 
appears on the second comparison signal line 509 the breakdown detecting 
comparison voltage derived through potential dividing by the resisters 506 
and 512 of a voltage which is lower by the corresponding threshold voltage 
V.sub.TN of the NMOS transistor 505 than the writing power supply voltage 
V.sub.PP. Such a breakdown detecting comparison voltage is fed to the 
comparator 42. In the writing mode,before the breakdown occurs on the 
antifuse 31, the writing power supply voltage V.sub.PP appears on the 
constant-current supply line 36. Therefore, the comparator outputs an "H" 
level of signal. When the breakdown occurs on the antifuse 31, a lower 
voltage than the breakdown detecting comparison voltage appears on the 
constant-current supply line 36. As a result, the output of the comparator 
42 reverses in the level to the "L" level. This "L" level of signal is 
delayed by, for example, 2.mu. sec, through the delay circuit 48 and 
transferred to one of the inputs of the AND gate 49. At that time, an "H" 
level of program signal PROG is shut out, so that the NMOS transistor 406 
turns off thereby shutting out the current flowing through the resister 
403. In other words, at that time, the writing current is restricted to 
only the current which flows through the resister 402. 
According to the embodiment shown in FIG. 10, in a similar fashion to that 
of the embodiment shown in FIG. 1, even if the respective antifuses 31 are 
mutually different in time up to the breakdown, writing is performed 
according to the different breakdown time. Thus, it is possible to more 
uniform and stable resistance value of filaments. 
As explained above, according to the present invention, it is possible to 
form stable filaments which are small in resistance value and less in 
disunity, and also possible to implement high speed operations of the PLD 
and the PROM. Further, according to the present invention, it is possible 
to produce high reliable chips, since it hardly involves malfunction 
because the timing skew of the PLD and the PROM is less, and further it 
involves no switch off in mid course of the operation. 
Furthermore, according to the present invention, there is provided a 
programmable semiconductor device, having a constant-voltage power supply 
terminal for writing, capable of easily writing with a technique similar 
to that of writing into, for example, the usual RAM and the like. 
While the present invention has been described with reference to the 
particular illustrative embodiments, it is not to be restricted by those 
embodiments but only by the appended claims. It is to be appreciated that 
those skilled in the art can change or modify the embodiments without 
departing from the scope and spirit of the present invention.