JP5668519B2 - Write control circuit and semiconductor device - Google Patents

Description

  The present invention relates to a write control circuit and a semiconductor device that control writing to a memory element that is electrically written only once.

  In recent years, in a RAM (Random Access Memory) circuit or the like, electric fuse elements are increasingly used for redundancy processing for relieving defective bits, identification numbers for identifying each chip, and the like.

  The electrical fuse element is a storage element (hereinafter referred to as an OTP (One Time Programming) element) in which writing is performed only once electrically. The electric fuse element is connected to a terminal to which a predetermined write voltage is applied and a write transistor. When a predetermined write voltage is applied and a write control signal such as a WE (Write Enable) signal is turned on, a current flows through the electric fuse element. The electric fuse element is cut by this current, and a write state is entered.

For this reason, erroneous writing may occur when an unintended current flows through the electric fuse element other than when writing is performed.
Conventionally, when a write target fuse is cut, the voltage of the write line rises, and other fuses are also cut to prevent erroneous writing, so that the voltage of the write line does not exceed a certain voltage. There was a technique to clamp.

  In addition, in order to prevent erroneous disconnection of an electrical fuse element when ESD (Electrostatic Discharge) occurs, a technique for preventing a surge current from flowing into the electrical fuse element by providing a diode for flowing an ESD surge current is known.

JP-A-53-007142 JP 2009-177044 A

  When an abnormality occurs in the writing voltage and the overvoltage occurs, the signal for controlling the writing transistor may be affected, and there is a problem that erroneous writing occurs. For example, even when not at the time of a write operation, the write transistor cannot be kept off due to a malfunction of a circuit that controls the write transistor, and there is a possibility that a current flows through the OTP element as described above.

According to one aspect of the invention, electrically writing only once driven by the write voltage supplied to the storage element to be performed, in response to a write signal, a write control unit for controlling the writing into the memory element , A voltage detection unit that is driven by the write voltage, detects the write voltage, and causes the write control unit to stop writing to the storage element regardless of the write signal when the write voltage exceeds a predetermined threshold voltage A write control circuit is provided.

A storage element that is electrically written only once, and a write transistor that is connected to the storage element and controls whether or not a current caused by a write voltage flows through the storage element in accordance with a control signal; Driven by the write voltage , outputs the control signal according to a write signal, and controls the writing to the memory element, and is driven by the write voltage, detects the write voltage, and writes the write There is provided a semiconductor device including a voltage detection unit that causes the write control unit to stop writing to the memory element regardless of the write signal when the voltage becomes equal to or higher than a predetermined threshold voltage.

  According to the disclosed write control circuit and semiconductor device, erroneous writing to a memory element in which writing is performed only once can be suppressed.

1 is a diagram illustrating an example of a semiconductor device and a write control circuit according to a first embodiment; 6 is a diagram illustrating an example of a semiconductor device and a write control circuit according to a second embodiment; FIG. It is a figure which shows an example of the signal waveform of each part at the time of the write-in operation | movement of a semiconductor device when a write voltage is normal. It is a figure which shows an example of the mode of the signal of a voltage detection part in case a write voltage becomes overvoltage. It is a figure which shows an example of the semiconductor device and write-in control circuit of 3rd Embodiment. It is a figure which shows an example of the mode of the signal of a voltage detection part in case a write voltage becomes overvoltage.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In the following, an example in which an electrical fuse element is used as an example of an OTP element that performs electrical writing will be described. However, the present invention is not limited to this. For example, a high voltage is applied to the gate oxide film of a transistor to electrically destroy it. Thus, an OTP element that is in a writing state may be used.

(First embodiment)
FIG. 1 is a diagram illustrating an example of a semiconductor device and a write control circuit according to the first embodiment.
The semiconductor device 1 includes an electric fuse element 2, a write transistor 3, and a write control circuit 10. The write control circuit 10 includes a write control unit 11 and a voltage detection unit 12.

  The electrical fuse element 2 and the write transistor 3 are connected, for example, between a terminal P1 to which a write voltage is applied from a tester circuit (not shown) and a ground terminal P2 that is a ground potential (reference potential).

  As the electric fuse element 2, an element using a silicide layer formed on a polysilicon layer, a metal fuse, or the like is used. When the electric fuse element 2 has a resistance value of 200Ω and is cut when a current of 10 mA flows, for example, about 3 V is applied as a write voltage.

  The write transistor 3 receives a control signal from the write control unit 11 and controls whether or not a current flows to the electric fuse element 2. In the example of FIG. 1, the write transistor 3 is an n-channel MOSFET (Metal-Oxide Semiconductor Field Effect Transistor).

  In the example shown in FIG. 1, one terminal of the electrical fuse element 2 is connected to a terminal P1 to which a write voltage is applied, and the other terminal is connected to one input / output terminal (drain) of the write transistor 3. Yes. The other input / output terminal (source) of the write transistor 3 is connected to the ground terminal P2, which is the ground potential, and a control signal from the write control unit 11 is input to the control terminal (gate).

  In the write control circuit 10, the write control unit 11 controls writing to the electrical fuse element 2 in accordance with, for example, a write signal input from a tester circuit (not shown) via the terminal P3. The write controller 11 controls writing to the electrical fuse element 2 by generating a control signal for turning on or off the write transistor 3 in accordance with, for example, a WE (Write Enable) signal that is a write signal. The write control unit 11 is driven by a write voltage supplied from the terminal P1. The write controller 11 is also connected to a ground terminal P2 that is a ground potential.

  The voltage detector 12 is connected to the terminal P1 and the ground terminal P2, and detects a write voltage supplied to the electrical fuse element 2. When the write voltage becomes equal to or higher than the predetermined threshold voltage, the voltage detection unit 12 causes the write control unit 11 to stop writing to the electrical fuse element 2 regardless of the write signal input to the write control unit 11. In the example shown in FIG. 1, the voltage detection unit 12 sends a signal for fixing the control terminal of the write transistor 3 to a potential of L (Low) level to the write control unit 11 (details will be described later). .

Although an example of the threshold voltage will be described later, when the write voltage is 3 V, for example, 3.3 V is set.
The write control circuit 10 as described above can maintain the write transistor 3 in the OFF state even when the write voltage becomes an overvoltage that is equal to or higher than a predetermined threshold voltage, and erroneous writing can be prevented.

  For example, when an abnormality occurs in the writing voltage when the writing voltage is turned on or when an adjacent circuit is operated, an overvoltage may occur, and the noise accompanying the abnormality may also cause an abnormality in the writing signal input from the terminal P3. There is. For example, when writing is performed with a pulse write signal having a H (High) level for a certain period, a waveform abnormality or the like occurs in the write signal due to an overvoltage, and the write signal becomes H level even though it should not be written. Incorrect writing may occur. In addition, when the write voltage is overwritten when the write voltage is overvoltage, a large amount of current flows through the electric fuse element 2 and the state can be overwritten.

  However, according to the write control circuit 10 of the present embodiment, when the write voltage becomes an overvoltage and becomes equal to or higher than a predetermined threshold voltage, the voltage detection unit 12 writes the electric fuse element 2 regardless of the write signal. The writing control unit 11 is stopped. In the example illustrated in FIG. 1, the voltage detection unit 12 fixes the control signal input from the write control unit 11 to the control terminal of the write transistor 3 at the L level.

  Thereby, even if the write voltage becomes an overvoltage equal to or higher than a predetermined threshold voltage, the write transistor 3 can be maintained in an off state, and a current can be prevented from flowing through the electric fuse element 2 and being cut. Incorrect writing and overwriting can be suppressed.

Hereinafter, an example of the write control circuit 10 will be described in more detail as the second embodiment and the third embodiment.
(Second Embodiment)
FIG. 2 is a diagram illustrating an example of a semiconductor device and a write control circuit according to the second embodiment.

The same elements as those of the semiconductor device 1 of the first embodiment are denoted by the same reference numerals and the description thereof is omitted.
In the semiconductor device 1a of the second embodiment, the write control circuit 10a includes a write control unit 11a and a voltage detection unit 12a.

The write control unit 11a includes an inverter circuit 111 and a NAND circuit 112.
The inverter circuit 111 inverts the signal level of the output signal of the NAND circuit 112 and outputs it as a control signal for the write transistor 3.

  The NAND circuit 112 outputs the NAND logic of the output signal of the voltage detector 12a and the write signal from the terminal P3. The NAND circuit 112 invalidates the write signal by the L level output signal output from the voltage detection unit 12a when the write voltage is equal to or higher than the threshold voltage. That is, the NAND circuit 112 outputs an H level signal regardless of the write signal.

The inverter circuit 111 and the NAND circuit 112 are connected to the terminal P1 and the ground terminal P2, and are driven by the write voltage.
The voltage detector 12a sets the threshold voltage described above based on the number of diodes connected in series between the terminal P1 and the ground terminal P2 and the forward voltage of the diode. In the example illustrated in FIG. 2, the voltage detection unit 12 a includes a transistor 121, diodes 122, 123, 124, 125 and resistors 126, 127.

  In the example of FIG. 2, the transistor 121 is an n-channel MOSFET, the drain is connected to the terminal P1 via the resistor 126, and the source is connected to the ground terminal P2. The gate (control terminal) is connected between the plurality of diodes 122 to 125. In the example of FIG. 2, it is connected to a node N <b> 1 between the cathode of the diode 124 and the anode of the diode 125.

  The diodes 122 to 125 are connected in series between the terminal P1 and the ground terminal P2. For example, when the forward voltage Vf of each of the diodes 122 to 125 is 0.8V, the above-described threshold voltage is 0.8 × 4 = 3.2V.

The resistor 126 adjusts the output voltage of the voltage detection unit 12a. For example, the resistor 126 is about 100 times the on-resistance of the transistor 121.
The resistor 127 has one terminal connected to the node N1 and the other terminal connected to the ground terminal P2. The resistor 127 is provided to drop the potential of the node N1 to the ground potential so as not to be in a floating state when the diodes 122 to 125 are in the off state. The resistor 127 is, for example, sufficiently large (for example, about 100 times) with respect to the on-resistance of the diode 125.

Hereinafter, the operation of the semiconductor device 1a according to the second embodiment will be described.
When the write voltage is applied to the terminal P1, for example, when the forward voltage Vf of each of the diodes 122 to 125 is 0.8V, the diodes 122 to 125 are in an off state when the write voltage is not about 3.2V or higher. Almost no current flows. Therefore, the potential of the node N1 becomes L level. At this time, since the transistor 121 is in an off state, the output signal of the voltage detection unit 12a taken out from the drain of the transistor 121 becomes H level.

  In the write control unit 11a, when an output signal of H level is input from the voltage detection unit 12a, when the write signal becomes H level, the output signal of the NAND circuit 112 becomes L level and the output signal of the inverter circuit 111 becomes H level. Become a level. As a result, the write transistor 3 is turned on, a current due to the write voltage flows, and writing to the electrical fuse element 2 is performed. When the write signal is at the L level, the output signal of the NAND circuit 112 is at the H level, and the output signal of the inverter circuit 111 is at the L level. At this time, the write transistor 3 is turned off, and writing to the electrical fuse element 2 is stopped.

  When the write voltage is about 3.2 V or more, in the voltage detection unit 12a, the diodes 122 to 125 are turned on, current flows, and the transistor 121 is turned on by the voltage applied to the diode 125 and the resistor 127.

  Note that when the value of the resistor 127 is sufficiently larger than the on-resistance of the diode 125, the transistor 121 is turned on by the forward voltage Vf of the diode 125 (for example, 0.8 V).

  When the transistor 121 is turned on, the output signal of the voltage detector 12a taken out from the drain of the transistor 121 becomes L level. This output signal is a signal that invalidates the write signal.

  That is, the NAND circuit 112 of the write control unit 11a outputs an H level output signal regardless of the state of the write signal. At this time, since the output signal of the inverter circuit 111 is at the L level, the write transistor 3 is turned off, and writing to the electrical fuse element 2 is stopped.

FIG. 3 is a diagram illustrating an example of a signal waveform of each unit during a write operation of the semiconductor device when the write voltage is normal.
The horizontal axis indicates time, and the vertical axis indicates voltage. From the top, the abnormality detection voltage (the aforementioned threshold voltage), the write voltage, the output signal of the voltage detection unit 12a, the potential of the node N1, the write signal, and the gate voltage of the write transistor 3 are shown.

  In the case of the write detection circuit 10a shown in FIG. 2, the abnormality detection voltage is, for example, 3.2V. In the normal case, the write voltage is smaller than the abnormality detection voltage as shown in FIG. Further, since the diodes 122 to 125 are in the off state, the potential of the node N1 is 0V. Therefore, the transistor 121 is in an off state, and the output voltage of the voltage detection unit 12a is at the H level.

  In this state, when the write signal is at the L level, the gate voltage of the write transistor 3 becomes 0 V by the operations of the NAND circuit 112 and the inverter circuit 111 described above. Therefore, the write transistor 3 is in an off state, and writing to the electrical fuse element 2 is not performed.

  When the write signal becomes H level (timing t1 in FIG. 3), the output signal of the NAND circuit 112 is inverted to L level, so that the gate voltage of the write transistor 3 becomes H level. Therefore, the write transistor 3 is turned on, current flows, and writing to the electrical fuse element 2 is performed. That is, cutting of the electric fuse element 2 is started.

  When the write signal falls to L level (0V) after a certain time (timing t2 in FIG. 3), the output signal of the NAND circuit 112 is inverted to H level, so that the gate voltage of the write transistor 3 becomes L level. . Therefore, the write transistor 3 is turned off, the current is interrupted, and writing to the electrical fuse element 2 is completed.

FIG. 4 is a diagram illustrating an example of a signal state of the voltage detection unit when the write voltage is an overvoltage.
The horizontal axis indicates time, and the vertical axis indicates voltage.

  When the write voltage becomes equal to or higher than the abnormality detection voltage (timing t3 in FIG. 4), the diodes 122 to 125 are turned on, and the potential of the node N1 is a voltage approximately equal to the forward voltage Vf of the diode 125 (for example, about 0.8V). ) Thereby, the transistor 121 is turned on, and the output signal of the voltage detection unit 12a becomes L level.

Thereby, the write control unit 11a turns off the write transistor 3 and does not write to the electrical fuse element 2 regardless of the state of the write signal.
When the write voltage becomes smaller than the abnormality detection voltage (timing t4 in FIG. 4), the diodes 122 to 125 are turned off, and the potential of the node N1 falls to 0V. Thereby, the transistor 121 is turned off, the output signal of the voltage detection unit 12a becomes H level, and the writing control unit 11a performs writing according to the state of the writing signal.

  As described above, according to the write control circuit 10a of the second embodiment, when an abnormality occurs in the write voltage and becomes equal to or higher than the predetermined threshold voltage (abnormality detection voltage), the electric fuse element regardless of the state of the write signal. Since writing to 2 is stopped, erroneous writing can be prevented.

In addition, the circuit scale can be reduced by setting the threshold voltage using a plurality of diodes connected in series.
In the example illustrated in FIG. 2, the case where the four diodes 122 to 125 are provided has been described. However, the number of diodes can be appropriately changed according to the threshold voltage to be set and the forward voltage Vf of the diode.

  In the example shown in FIG. 2, the transistor 121 is turned on by the voltage applied to the diode 125 when each diode 122 to 125 is turned on and a forward current flows. However, the present invention is not limited to this. . The connection position of the control terminal of the transistor 121 between the diodes 122 to 125 is appropriately set according to the forward voltage Vf of each diode 122 to 125 so that the transistor 121 is also turned on when the diodes 122 to 125 are turned on. It may be changed.

(Third embodiment)
FIG. 5 is a diagram illustrating an example of a semiconductor device and a write control circuit according to the third embodiment.
Elements that are the same as those of the semiconductor device 1a of the second embodiment shown in FIG.

In the semiconductor device 1b of the third embodiment, the voltage detection unit 12b of the write control circuit 10b is different from the voltage detection unit 12a of the second embodiment.
The voltage detection unit 12b includes a threshold voltage generation circuit 128 and a comparison circuit 129.

  The threshold voltage generation circuit 128 generates a predetermined threshold voltage used as an abnormality detection voltage. The threshold voltage generation circuit 128 includes, for example, a constant voltage generation circuit in which a plurality of transistors are combined, a plurality of diodes connected in series as shown in FIG. 2, a Zener diode, or the like, and generates a desired threshold voltage. For example, a plurality of series circuits having different numbers of connected diodes may be provided, and the threshold voltage may be adjusted by selecting one of the series circuits based on a signal from a tester circuit (not shown).

  The negative input terminal of the comparison circuit 129 is connected to the terminal P1, and the positive input terminal is connected to the threshold voltage generation circuit 128. When the write voltage applied to the terminal P1 is equal to or higher than the threshold voltage generated by the threshold voltage generation circuit 128, the comparison circuit 129 outputs a signal for invalidating the write signal in the write control unit 11a. In the example shown in FIG. 5, the comparison circuit 129 outputs an L level output signal that invalidates the write signal.

The threshold voltage generation circuit 128 and the comparison circuit 129 are connected between the terminal P1 and the ground terminal P2, respectively, and are driven by the write voltage.
In such a write control circuit 10b, when the write voltage is smaller than the threshold voltage, the output signal of the voltage detector 12b is the same as the operation waveform of the semiconductor device 1a of the second embodiment shown in FIG. Then, it becomes H level. The write controller 11a performs writing according to the state of the write signal.

When the write voltage is equal to or higher than the threshold voltage output from the threshold voltage generation circuit 128, the following operation is performed.
FIG. 6 is a diagram illustrating an example of a signal state of the voltage detection unit when the write voltage is an overvoltage.

The horizontal axis indicates time, and the vertical axis indicates voltage.
When the writing voltage becomes equal to or higher than the abnormality detection voltage (threshold voltage) (timing t5 in FIG. 6), the output of the comparison circuit 129, that is, the output signal of the voltage detection unit 12b becomes L level.

Thereby, the write control unit 11a turns off the write transistor 3 and does not write to the electrical fuse element 2 regardless of the state of the write signal.
When the write voltage becomes smaller than the abnormality detection voltage (timing t6 in FIG. 6), the output of the comparison circuit 129, that is, the output signal of the voltage detection unit 12b becomes H level, and the write control unit 11a performs writing according to the state of the write signal. Done.

  As described above, according to the write control circuit 10b of the third embodiment, when an abnormality occurs in the write voltage and becomes equal to or higher than the predetermined threshold voltage (abnormality detection voltage), the electric fuse element regardless of the state of the write signal. Since writing to 2 is stopped, erroneous writing can be prevented.

Further, a desired threshold voltage can be set by the threshold voltage generation circuit 128.
As described above, one aspect of the write control circuit and the semiconductor device of the present invention has been described based on the embodiment, but these are merely examples, and the present invention is not limited to the above description.

For example, a plurality of electrical fuse elements may be provided. In that case, a write control circuit 10, 10a, 10b is provided for each electrical fuse element and write transistor.
Further, the write transistor 3 and the transistor 121 may be p-channel MOSFETs. In that case, the circuit configuration is changed as appropriate. A bipolar transistor may be used instead of the MOSFET.

  Further, as another configuration in which a plurality of electrical fuse elements are provided, a configuration in which the voltage detection units 12, 12a, and 12b are shared with respect to each electrical fuse element, the write transistor, and the write control unit in the write control circuit is applied. May be.

DESCRIPTION OF SYMBOLS 1 Semiconductor device 2 Electrical fuse element 3 Write transistor 10 Write control circuit 11 Write control part 12 Voltage detection part P1, P3 terminal P2 Ground terminal

Claims (6)

Driven by electrical writing voltage writing only once supplied to the storage element to be performed, in response to a write signal, a write control unit for controlling the writing into the memory element,
A voltage detection unit that is driven by the write voltage, detects the write voltage, and causes the write control unit to stop writing to the storage element regardless of the write signal when the write voltage exceeds a predetermined threshold voltage; ,
A write control circuit comprising:   The write control unit includes a logic circuit that invalidates the write signal by a signal output from the voltage detection unit when the write voltage is equal to or higher than the threshold voltage. The write control circuit described.   The voltage detector includes a plurality of diodes connected in series between a ground terminal and a terminal to which the write voltage is applied, and the threshold voltage is set by the number of the diodes and a forward voltage. The write control circuit according to claim 1 or 2, characterized in that:   The voltage detection unit is connected between the ground terminal and a terminal to which the write voltage is applied, a control terminal is connected between the plurality of diodes, and a signal that invalidates the write signal from one input / output terminal. 4. The write control circuit according to claim 3, further comprising a transistor that outputs to the write control unit.   The voltage detection unit compares a threshold voltage generation circuit that generates the threshold voltage, and compares the write voltage with the threshold voltage, and outputs a signal that invalidates the write voltage when the write voltage exceeds the threshold voltage. The write control circuit according to claim 1, further comprising: a comparison circuit that outputs to the write control unit. A storage element that is electrically written only once;
A write transistor that is connected to the storage element and controls whether or not a current caused by a write voltage flows through the storage element in accordance with a control signal;
A write controller that is driven by the write voltage and outputs the control signal according to a write signal to control writing to the storage element;
A voltage detection unit that is driven by the write voltage, detects the write voltage, and causes the write control unit to stop writing to the storage element regardless of the write signal when the write voltage exceeds a predetermined threshold voltage; ,
A semiconductor device comprising:

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