JP2018198108A - Semiconductor device - Google Patents

Abstract

To provide a semiconductor device that prevents a test from being passed, which, when a failure is found in a memory cell, gives a test result according to an expected value in testing irrespective of no potential difference in a bit line pair.SOLUTION: A word line WL is connected to a mask ROM memory cell CL, and a bit line pair Bit, Bitn is connected to the memory cell CL. A differential sense amplifier 503 amplifies a potential difference of the bit line pair Bit, Bitn. A logical circuit 505 detects coincidence or non-coincidence of logical states of the bit line pair Bit, Bitn.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a semiconductor device, and more particularly to a semiconductor device including a mask ROM (Read Only Memory).

  In Patent Document 1, a memory cell is composed of a pair of MOS transistors having different threshold voltages. In this memory cell, data of logic “1” and “0” is fixedly programmed depending on which threshold value of a pair of MOS transistors is set higher. A pair of MOS transistors is connected to a pair of bit lines. The complementary level of the pair of bit lines is given to the differential amplifier via the common data line. The differential sense amplifier detects the level difference of the input signal, amplifies it, and outputs it as external memory cell data.

Japanese Unexamined Patent Publication No. 1-100797

  However, even if the differential sense amplifier is designed to have a completely symmetrical circuit layout, there are variations in pairs due to impurity fluctuations, etc. Depending on the finished state, it is misjudged. In other words, even if the bit line pair has the same potential, the differential sense amplifier outputs a value determined by the polarity of the offset voltage.

  That is, when there is a failure in a memory cell (for example, the connection between the memory cell and the bit line is broken), even if no potential difference occurs between the bit line pair, a series of LSI shipping tests (especially in the mask ROM) In the manufacturing defect determination test, the determination may be made as expected, and the test may be passed. However, there is a risk that a malfunction may become apparent due to noise in the market.

  Other problems and novel features will be apparent from the description of this specification and the accompanying drawings.

  A semiconductor device according to an embodiment includes a plurality of mask ROM memory cells, a first bit line and a second bit line connected to the plurality of mask ROM memory cells, and a first bit and a second bit. A differential sense amplifier that amplifies the potential difference between the lines and a logic circuit that detects a match or mismatch of the logic states of the first and second bit lines.

  According to one embodiment, when there is a failure in a memory cell, it is possible to prevent the test from being passed by making a determination as expected when testing.

It is a figure showing the structure of the semiconductor device of 1st Embodiment. It is a figure showing the structure of the semiconductor device of 2nd Embodiment. It is a figure showing the structure of an internal clock generation circuit. It is a figure for demonstrating the pulse width of internal clock CLKB produced | generated at the time of normal mode. It is a figure for demonstrating the pulse width of the internal clock CLKB produced | generated at the time of a test mode. FIG. 10 is a diagram illustrating a partial configuration in an i-th column of a memory array and an I / O circuit according to a second embodiment. It is a figure showing the structure of a differential sense amplifier. It is a figure for demonstrating operation | movement of a differential sense amplifier. In 2nd Embodiment, it is a figure showing the time change of the signal produced | generated at the time of normal mode. It is a figure showing the time change of the signal produced | generated at the time of a test mode in 2nd Embodiment. FIG. 10 is a diagram illustrating a partial configuration in an i-th column of a memory array and an I / O circuit according to a third embodiment. In 3rd Embodiment, it is a figure showing the time change of the signal produced | generated by the 1st phase at the time of test mode. In 3rd Embodiment, it is a figure showing the time change of the signal produced | generated by the 2nd phase at the time of test mode. It is a figure showing the one part structure in the i-th column of the memory array and I / O circuit in 4th Embodiment. In 4th Embodiment, it is a figure showing the time change of the signal produced | generated by the 1st phase at the time of test mode. In 4th Embodiment, it is a figure showing the time change of the signal produced | generated by the 2nd phase at the time of test mode. FIG. 10 is a diagram illustrating a partial configuration in an i-th column of a memory array and an I / O circuit according to a fifth embodiment. It is a figure showing the time change of the signal produced | generated at the time of a test mode in 5th Embodiment.

Hereinafter, embodiments will be described with reference to the drawings.
[First Embodiment]
FIG. 1 is a diagram illustrating the configuration of the semiconductor device according to the first embodiment.

  The semiconductor device includes a plurality of mask ROM memory cells CL, a word line WL, a bit line pair Bit and Bitn, a differential sense amplifier 503, an output latch 504, and a logic circuit 505.

The word line WL is connected to the memory cell CL.
The bit line pair Bit, Bitn is connected to the memory cell CL.

The differential sense amplifier 503 amplifies the potential difference between the bit line pair Bit and Bitn.
The logic circuit 505 is connected to the bit line pair Bit, Bitn. The logic circuit 505 detects the match or mismatch of the logic states of the bit line pair Bit and Bitn.

The output latch 504 latches the output of the logic circuit 505.
As described above, according to the present embodiment, by providing a logic circuit connected to the bit line pair, when there is a failure in the memory cell for the mask ROM, a determination is made as expected during the test, As a result, the test can be prevented from passing.
[Second Embodiment]
FIG. 2 is a diagram illustrating the configuration of the semiconductor device according to the second embodiment.

  Referring to FIG. 2, the semiconductor device includes an address predecoder 101, a control circuit 102, a row decoder 103, a memory array 104, and an I / O circuit 107.

  The address predecoder 101 includes a plurality of latches 110-1 to 110- that hold different bits of the address signal A, and a predecode that decodes the bits of the address signal A output from the latches 110-1 to 110-5. Decoders 111-1 to 111-5 are provided.

  Memory array 104 includes a plurality of mask ROM memory cells arranged in a matrix.

  The row decoder 103 selects one of the plurality of word lines WL in the memory array 104 according to the decoding results of the predecoders 111-1 to 111-5, and activates the selected word line WL.

  The control circuit 102 includes a latch 110a, an internal clock generation circuit 112, and a control logic circuit 108.

  The latch 110a latches the control signal from the control logic circuit 108 when the clock enable signal CEN is enabled.

  The internal clock generation circuit 112 generates an internal clock CLKB from the external clock CLK, and supplies the internal clock CLKB to the control logic circuit 108 and the like.

  The control logic circuit 108 controls the operation (test signal level) in the test mode (first mode). The control logic circuit 108 receives a mode switching signal for switching between a test mode and a normal mode to be described later from the outside of the mask ROM, and generates an internal control signal (Test, (Test1, Test2), etc.) when switched to the test mode. .

  The I / O circuit 107 includes a precharge circuit + CSL driver group 105, a column selector group 106, a differential sense amplifier group 310, and an output latch group 211.

FIG. 3 is a diagram showing the configuration of internal clock generation circuit 112.
As shown in FIG. 3, the internal clock generation circuit 112 includes an inverter 51, an inverter 52, a NAND circuit 53, a NAND circuit 54, an inverter 55, and a delay circuit 56.

  Inverter 51 receives external clock CLK and outputs a signal obtained by inverting external clock CLK.

  Inverter 52 receives the output of inverter 51 and outputs a signal MKPLSD obtained by inverting the output of inverter 51.

  The NAND circuit 53 receives a signal PGE generated by the control logic circuit 108 receiving a mode switching signal from the outside of the mask ROM and the signal MKPLSD, and outputs a negative logical product of the signal PGE and the signal MKPLSD.

The delay circuit 56 receives the output of the NAND circuit 53 and outputs a signal PLSW.
NAND circuit 54 receives external clock CLK and signal PLSW, and outputs a negative logical product of external clock CLK and signal PLSW.

  Inverter 55 receives the output of NAND circuit 54 and outputs internal clock CLKB obtained by inverting the output of NAND circuit 54.

  FIG. 4 is a diagram for explaining the pulse width of the internal clock CLKB generated in the normal mode (second mode). Here, the normal mode is a mode for performing normal operation and a mode for testing a state during normal operation in a shipping test.

  When the external clock CLK rises, the internal clock CLKB rises after a delay time (α1) by the NADN circuit 54 and the inverter 55.

  On the other hand, when the external clock CLK rises, the signal MKPLSD rises after the delay time (α2) by the inverters 51 and 52. In the normal mode, since PGE is at “H” level, the signal PLSW falls after the delay time (DELAY) by the delay circuit 56. Thereafter, the internal clock CLKB falls after the delay time (α1) by the NADN circuit 54 and the inverter 55 from the fall of the signal PLSW.

  Therefore, the length of the period during which the internal clock CLKB is at the high level is DELAY + α1.

  FIG. 5 is a diagram for explaining the pulse width of the internal clock CLKB generated in the test mode.

  When the external clock CLK rises, the internal clock CLKB rises after a delay time (α1) by the NADN circuit 54 and the inverter 55.

  On the other hand, when the external clock CLK rises, the signal MKPLSD rises after the delay time (α2) by the inverters 51 and 52. In the test mode, since PGE is at “L” level, signal PLSW maintains “H” level.

  When external clock CLK falls, signal PLSW is at “H” level, so that internal clock CLKB falls after delay time (α1) by NADN circuit 54 and inverter 55.

  Therefore, the period during which internal clock CLKB is at the high level is the length (DT) of the period during which external clock CLK is at the “H” level.

  FIG. 6 is a diagram illustrating a partial configuration in the i-th column of the memory array 104 and the I / O circuit 107 in the second embodiment.

  Referring to FIG. 6, the i-th column of memory array 104 includes a plurality of memory cells. In the present embodiment, three memory cells CL_000, CL_xxx, and CL_yyy are representatively shown.

  The memory array 104 includes word lines WL_000, WL_xxx, WL_yyy connected to the memory cells CL_000, CL_xxx, CL_yyy, bit lines Bit, Bitn, a source line SL, and a switch 161.

The switch 161 connects the source line SL to the power supply vdd or the ground GND.
Memory cell CL_000 includes N-channel MOS transistors TR-A and TR-B. N-channel MOS transistor TR-A is provided between node N1_000 on bit line Bit and node S_000 on source line SL. The gate of N-channel MOS transistor TR-A is connected to word line WL_000. N-channel MOS transistor TR-B is provided between node N2_000 on bit line Bitn and node S_000 on source line SL. The gate of N-channel MOS transistor TR-B is connected to word line WL_000.

  Here, a program contactor exists between N-channel MOS transistor TR-A and node S_000 on source line SL. Therefore, when N channel MOS transistor TR-A is on, the voltage on source line SL is transmitted to bit line Bit via N channel MOS transistor TR-A.

  On the other hand, there is no program contactor between N-channel MOS transistor TR-B and node S_000 on source line SL. Therefore, when N channel MOS transistor TR-B is on, the voltage on source line SL is not transmitted to bit line Bitn via N channel MOS transistor TR-B.

  Memory cell CL_xxx includes N-channel MOS transistors TR-1 and TR-2. N-channel MOS transistor TR-1 is provided between node N1_xxx on bit line Bit and node S_xxx on source line SL. The gate of N-channel MOS transistor TR-1 is connected to word line WL_xxx. N-channel MOS transistor TR-2 is provided between node N2_xxx on bit line Bitn and node S_xxx on source line SL. The gate of N-channel MOS transistor TR-2 is connected to word line WL_xxx.

  Here, a program contactor exists between N-channel MOS transistor TR-1 and node S_xxx on source line SL. Therefore, when N channel MOS transistor TR-1 is on, the voltage on source line SL is transmitted to bit line Bit via N channel MOS transistor TR-1.

  On the other hand, there is no program contactor between N-channel MOS transistor TR-2 and node S_xxx on source line SL. Accordingly, when N channel MOS transistor TR-2 is on, the voltage on source line SL is not transmitted to bit line Bitn via N channel MOS transistor TR-2.

  Memory cell CL_yyy includes N-channel MOS transistors TR-C and TR-D. N-channel MOS transistor TR-C is provided between node N1_yyy on bit line Bit and node S_yyy on source line SL. The gate of N-channel MOS transistor TR-C is connected to word line WL_yyy. N-channel MOS transistor TR-D is provided between node N2_yyy on bit line Bitn and node S_yyy on source line SL. The gate of N-channel MOS transistor TR-D is connected to word line WL_yyy.

  Here, there is no program contactor between the N-channel MOS transistor TR-C and the node S_yyy on the source line SL. Therefore, when N channel MOS transistor TR-C is on, the voltage on source line SL is not transmitted to bit line Bit via N channel MOS transistor TR-C.

  On the other hand, a program contactor exists between N-channel MOS transistor TR-D and node S_yyy on source line SL. Therefore, when N channel MOS transistor TR-D is on, the voltage on source line SL is transmitted to bit line Bitn via N channel MOS transistor TR-D.

  A precharge circuit 50 for setting a bit line pair to a constant potential before activation of a word line includes P channel MOS transistors TR-3, TR-4, and TR-5. P-channel MOS transistor TR-3 is provided between power supply vdd and node ND1 on bit line Bit. The gate of P-channel MOS transistor TR-3 receives precharge signal PC. P-channel MOS transistor TR4 is provided between power supply vdd and node ND2 on bit line Bitn. The gate of P channel MOS transistor TR4 receives precharge signal PC. P-channel MOS transistor TR-5 is provided between node ND1 on bit line Bit and node ND2 on bit line Bitn. The gate of P channel MOS transistor TR4 receives precharge signal PC.

  The column selector 58 includes P-channel MOS transistors TR-6 and TR-7. P-channel MOS transistor TR-6 is provided between node N1_yyy on bit line Bit and node ND3. P-channel MOS transistor TR-6 is provided between node N2_yyy on bit line Bit and node ND4. The gates of P-channel MOS transistors TR-6 and TR-7 receive a column selection signal C_SEL <i>.

  The gate of P channel MOS transistor TR-6 and the gate of P channel MOS transistor TR-7 receive column selection signal C_SEL <i>.

  The differential sense amplifier 10 amplifies the voltage difference between the node ND3 on the bit line Bit and the node ND4 on the bit line Bitn.

The logic circuit 245 is connected to the bit line pair Bit, Bitn.
Logic circuit 245 includes inverters IV1 and IV2 and exclusive OR circuit EOR.

  Inverter IV1 is connected to node ND3 on bit line Bit and receives the voltage of bit line Bit. Inverter IV2 is connected to node ND4 on bit line Bitn and receives the voltage of bit line Bitn. The inverter IV1 and the inverter IV2 have the same characteristics, and the threshold voltage is the same.

  Here, since the column selector 58 is composed of P-channel MOS transistors TR-6 and TR-7, the inputs of the inverters IV1 and IV2 are input from the precharge level (vdd level) to the P-channel MOS transistor TR-6, It only decreases to a value smaller by the threshold voltage P_Vth of TR7. Therefore, the threshold voltages of inverters IV1 and IV2 are set higher than vdd / 2. When the column selector 58 is composed of CMOS transistors, the threshold voltages of the inverters IV1 and IV2 may be set to vdd / 2.

  Exclusive OR circuit EOR outputs a latch signal QT representing an exclusive OR of the output of inverter IV1 and the output of inverter IV2.

  The multiplexer MUX receives the output signal QT of the exclusive OR circuit EOR and the output signal QN of the differential sense amplifier 10. The multiplexer MUX outputs the signal QT when the test signal Test is activated to “H” level. The multiplexer MUX outputs the signal QN when the test signal Test is inactivated to the “L” level.

FIG. 7 is a diagram showing a configuration of differential sense amplifier 10 in the i-th column.
The differential sense amplifier 10 includes a precharge / equalize unit 220, an amplification unit 230, and a buffer unit 240.

  Precharge and equalize unit 220 has a P channel MOS transistor P3 for connecting data read line CTB and power supply voltage vdd, a P channel MOS transistor P4 for connecting data read line CBB and power supply voltage vdd, P channel MOS transistor P5 for connecting data read lines CTB and CBB is provided. The gates of P channel MOS transistors P3, P4 and P5 receive equalize signal EQB. Note that the equalize signal EQB is generated by the control logic circuit 108 (not shown).

  The amplifying unit 230 includes P-channel MOS transistors P6 and P7 and N-channel MOS transistors N1, N2, and N3.

  P-channel MOS transistor P6 is provided between power supply voltage vdd and node ND3 of data read line CTB. N channel MOS transistor N1 is provided between nodes ND3 and ND5 of data read line CTB. P-channel MOS transistor P7 is provided between power supply voltage vdd and node ND4 of data read line CBB. N channel MOS transistor N2 is provided between nodes ND4 and ND5 of data read line CBB. N-channel MOS transistor N3 is provided between node ND5 and ground GND.

  The gate of P channel MOS transistor P6 and the gate of N channel MOS transistor N1 are connected to node ND6. The gate of P channel MOS transistor P7 and the gate of N channel MOS transistor N2 are connected to node ND9. N channel MOS transistor N3 has its gate receiving sense amplifier activation signal SAE. When sense amplifier activation signal SAE is activated to “H” level, amplifying unit 230 performs an amplifying operation.

  Buffer unit 240 includes IV11, P-channel MOS transistors P8 and P10, and N-channel MOS transistors N5 and N6.

  Although not shown, the sense amplifier activation signal SAE is generated by the control logic circuit 108.

  P-channel MOS transistor P8 is provided between power supply voltage vdd and node ND7.

  N-channel MOS transistor N5 is provided between ground GND and node ND7.

  The gate of P channel MOS transistor P8 and the gate of N channel MOS transistor N5 are connected to data read line CTB.

  P-channel MOS transistor P10 and N-channel MOS transistor N6 are provided between power supply voltage vdd and ground GND. The gate of P channel MOS transistor P10 and the gate of N channel MOS transistor N6 are connected to data read line CBB.

Inverter IV11 receives a voltage at node ND7 and outputs a latch signal QN.
FIG. 8 is a diagram for explaining the operation of the differential sense amplifier.

Here, an operation focusing on the memory cell CL_xxx in FIG. 6 will be described.
When the word line WL_xxx is activated and the source line SL is connected to the ground GND, the potential of the bit line Bit decreases, and the potential of the bit line Bitn maintains the precharge level (vdd level).

  At this time, the column selection signal C_SEL <i> falls to the “L” level, and the equalize signal EQB rises to the “H” level. Thereby, P channel MOS transistors P1 and P2 are turned on, bit line Bit and data read line CTB are connected, and bit line Bitn and data read line CBB are connected. In addition, precharge and equalization of data read lines CBT and CBB by P channel MOS transistors P3, P4 and P5 are completed.

  The sense amplifier activation signal SAE is activated at the timing when the activation of the word line WL is completed. As a result, the amplification operation by the amplifying unit 230 starts, the voltage of the data read line CTB decreases to the “L” level, and the latch signal QN changes to the “L” level.

(Operation in normal mode)
FIG. 9 is a diagram illustrating a time change of a signal generated in the normal mode in the second embodiment.

  Here, paying attention to the memory cell CL_xxx in FIG. 6, the reading operation of the memory cell CL_xxx in the normal mode will be described.

  Although not shown, in the normal mode, the test signal Test is set to the “L” level by the control logic circuit 108.

  First, when the precharge signal PC is at the “L” level, the P-channel MOS transistors TR-3, TR-4, TR-5 are turned on, and the voltages of the bit line Bit and the bit line Bitn are set to the precharge level (vdd level). )

  When word line WL_xxx is inactive ("L" level), N-channel MOS transistors TR-1 and TR-2 are turned off, and the voltage of source line SL is not transmitted to bit line Bit and bit line Bitn. .

  Next, the precharge signal PC rises to the “H” level, the word line WL_xxx rises to the “H” level, and the switch 161 connects the source line SL to the ground GND. Here, the precharge circuit + CSL driver group 105 and the row decoder 103 activate the precharge signal PC and the word line WL_xxx based on the clock CLKB. Therefore, in the normal mode, the period during which the precharge signal PC and the word line WL_xxx are activated has the pulse width of the clock CLKB in the normal mode as shown in FIG. 4, and is shorter than in the test mode.

  When precharge signal PC rises to "H" level, P-channel MOS transistors TR-3, TR-4, TR-5 are turned off. Further, when the word line WL_xxx rises to the “H” level, the N-channel MOS transistors TR-A and TR-B are turned on.

  When the wiring between the N channel MOS transistor TR-1 and the source line SL is not disconnected, the voltage of the ground GND on the source line SL is changed to the bit line Bit via the N channel MOS transistor TR-1. Is transmitted. As a result, the voltage of the bit line Bit decreases.

  On the other hand, since there is no program contactor between N-channel MOS transistor TR-2 and node S_xxx on source line SL, the voltage on source line SL is applied to bit via N-channel MOS transistor TR-2. Not transmitted to the line Bitn, the voltage of the bit line Bitn maintains the precharge level (vdd level).

  The differential sense amplifier 10 amplifies a minute potential difference between the bit line Bit and the bit line Bitn. As a result, the voltage of data read line CTB decreases to “L” level, and latch signal QN becomes “L” level, although not shown.

  In the normal mode, since the test signal Test is at the “L” level, the multiplexer MUX supplies the latch signal QN output from the differential sense amplifier 10 to the output latch 11.

  The output latch 11 receives the “L” level latch signal QN and outputs an “L” level output signal Q.

  Here, when the wiring between the N-channel MOS transistor TR-1 and the source line SL is disconnected due to a defect in manufacturing, the voltage of the ground GND on the source line SL is changed to the N-channel MOS transistor. It is not transmitted to the bit line Bit via TR-1. As a result, as indicated by the broken line in FIG. 9, the voltage of the bit line Bit maintains the precharge level (vdd level).

  If the differential sense amplifier 10 has an offset that allows easy sensing when the bit line Bit is at the “L” level, the voltage of the data read line CTB decreases to the “L” level and is not shown. The latch signal QN becomes “L” level. As a result, the output signal Q from the output latch 11 becomes the “L” level as in the case where there is no defect during manufacture. Therefore, when this semiconductor device does not have a test mode as will be described later, the shipping test is passed.

  However, both N-channel MOS transistors TR-1 and TR-2 are not connected to the source line SL, and thus may be susceptible to noise during actual operation in the market. As a result, the output signal Q from the output latch 11 becomes unstable and may become “H” level, and there is a risk of malfunction.

(Operation in test mode)
FIG. 10 is a diagram illustrating a time change of a signal generated in the test mode in the second embodiment.

  Here, focusing on the memory cell CL_xxx in FIG. 6, detection of a program abnormality of the memory cell CL_xxx in the test mode will be described.

  Although not illustrated, in the test mode, the test signal Test is set to the “H” level by the control logic circuit 108.

  First, when the precharge signal PC is at the “L” level, the P-channel MOS transistors TR-3, TR-4, TR-5 are turned on, and the voltages of the bit line Bit and the bit line Bitn are set to the precharge level (vdd level). )

  When word line WL_xxx is inactive ("L" level), N-channel MOS transistors TR-1 and TR-2 are turned off, and the voltage of source line SL is not transmitted to bit line Bit and bit line Bitn. .

  Next, the precharge signal PC rises to the “H” level, the word line WL_xxx rises to the “H” level, and the switch 161 connects the source line SL to the ground GND.

  Here, the precharge circuit + CSL driver group 105 and the row decoder 103 activate the precharge signal PC and the word line WL_xxx based on the clock CLKB. Therefore, in the test mode, the period during which the precharge signal PC and the word line WL_xxx are activated has a pulse width of the clock CLKB in the test mode as shown in FIG. 5, and is longer than that in the normal mode.

  When precharge signal PC rises to "H" level, P-channel MOS transistors TR-3, TR-4, TR-5 are turned off. Further, when the word line WL_xxx rises to the “H” level, the N-channel MOS transistors TR-A and TR-B are turned on.

  When the wiring between the N channel MOS transistor TR-1 and the source line SL is not disconnected, the voltage of the ground GND on the source line SL is changed to the bit line Bit via the N channel MOS transistor TR-1. Is transmitted. As a result, the voltage of the bit line Bit decreases.

  On the other hand, since there is no program contactor between N-channel MOS transistor TR-2 and node S_xxx on source line SL, the voltage on source line SL is applied to bit via N-channel MOS transistor TR-2. Not transmitted to the line Bitn, the voltage of the bit line Bitn maintains the precharge level (vdd level).

  Even in the test mode, the differential sense amplifier 10 amplifies a minute potential difference between the bit line Bit and the bit line Bitn. However, in the test mode, the differential sense amplifier 10 may be stopped.

  Inverter IV1 outputs an “H” level when the voltage of bit line Bit decreases below the threshold voltage of inverter IV1. Conversely, in this embodiment, the row decoder 103 needs to activate the word line WL_xxx until the voltage of the bit line Bit becomes equal to or lower than the threshold voltage of the inverter IV1.

  On the other hand, the output of the inverter IV2 is maintained at “L” level because the voltage of the bit line Bitn maintains the precharge level (vdd level).

  The exclusive OR circuit EOR outputs “H”, which is the exclusive OR of the output of the inverter IV1 and the output of the inverter IV2, as the latch signal QT.

  In the test mode, since the test signal Test is at the “H” level, the multiplexer MUX supplies the output latch 11 with the “H” level latch signal QT output from the exclusive OR circuit EOR.

  The output latch 11 receives the “H” level latch signal QT and outputs an “H” level output signal Q.

  Here, when the wiring between the N-channel MOS transistor TR-1 and the source line SL is disconnected due to a defect in manufacturing, the voltage of the ground GND on the source line SL is changed to the N-channel MOS transistor. It is not transmitted to the bit line Bit via TR-1. As a result, as indicated by the broken line in FIG. 10, the voltage of the bit line Bit maintains the precharge level (vdd level).

  The output of the inverter IV1 maintains the “L” level because the voltage of the bit line Bit is the precharge level (vdd level). As a result, the latch signal QT output from the exclusive OR circuit EOR becomes “L” level, the latch signal QT output from the multiplexer MUX becomes “L” level, and the output signal Q output from the output latch 11 is “ L "level.

  By recognizing that the output signal Q having a level different from the normal level (expected value) is output from the output latch 11, the N-channel MOS transistor TR- 1 and the source line SL are connected to each other due to a defect in manufacturing. The wiring between them is broken, and it can be known that they are not programmed correctly.

  As described above, according to the present embodiment, in the test mode, it is possible to prevent the influence of the offset voltage of the differential sense amplifier by determining the voltage level of the bit line pair using the inverter. , Test accuracy can be improved.

  In the present embodiment, the expected value in the test mode is “1” for all addresses and does not depend on the program code, so that BIST (Built-In Self-Test) is easy.

  Further, in this embodiment, since the added circuits are only two inverters, an exclusive OR circuit, and a multiplexer, the overhead of the circuit area is small.

In this embodiment, the voltage of the bit lines Bit and Bitn is sensed using an inverter. However, the voltage of the bit lines Bit and Bitn can be sensed directly using an exclusive OR circuit or an NADN circuit. Good.
[Third Embodiment]
FIG. 11 is a diagram illustrating a partial configuration in the i-th column of the memory array 104 and the I / O circuit 107 in the third embodiment.

The configuration of FIG. 11 is different from the configuration of FIG. 6 as follows.
The configuration of FIG. 11 does not include the inverters IV1 and IV2 and the exclusive OR circuit EOR, and includes a voltage fixing circuit (voltage control circuit) 61 instead.

  The voltage fixing circuit 61 fixes the bit line Bit or Bitn to a voltage higher than the voltage of the ground GND and lower than the precharge voltage (vdd).

  The voltage fixing circuit 61 includes P channel MOS transistors TR-8 and TR-9.

  The P-channel MOS transistor TR-8 is provided between the node N_te1 on the bit line Bit and the ground GND. The gate of P channel MOS transistor TR-8 receives test signal Test2.

  P-channel MOS transistor TR-9 is provided between node N_te2 on bit line Bitn and ground GND. The gate of P channel MOS transistor TR-9 receives test signal Test1.

  The output latch 11 receives and latches the output signal QN of the differential sense amplifier 10 and outputs it as an output signal Q to the outside.

(Operation in normal mode)
The time change of the signal generated in the normal mode in the present embodiment is the same as that in the second embodiment shown in FIG. Therefore, the time change of the signal generated in the normal mode in the present embodiment will be described with reference to FIG.

  Here, paying attention to the memory cell CL_xxx in FIG. 11, the reading operation of the memory cell CL_xxx in the normal mode will be described.

  Although not shown, in the normal mode, the test signals Test 1 and Test 2 are set to “H” level by the control logic circuit 108.

  First, when the precharge signal PC is at the “L” level, the P-channel MOS transistors TR-3, TR-4, TR-5 are turned on, and the voltages of the bit line Bit and the bit line Bitn are at the precharge level (vdd level). It becomes.

  When word line WL_xxx is inactive ("L" level), N-channel MOS transistors TR-1 and TR-2 are turned off, and the voltage of source line SL is not transmitted to bit line Bit and bit line Bitn. .

  Next, the precharge signal PC rises to the “H” level, the word line WL_xxx rises to the “H” level, and the switch 161 connects the source line SL to the ground GND. Here, the precharge circuit + CSL driver group 105 and the row decoder 103 activate the precharge signal PC and the word line WL_xxx based on the clock CLKB. Therefore, in the normal mode, the period during which the precharge signal PC and the word line WL_xxx are activated has the pulse width of the clock CLKB in the normal mode as shown in FIG. 4, and is shorter than in the test mode.

  In the normal mode, since the test signals Test1 and Test2 are at “H” level, the P-channel MOS transistors TR-8 and TR-9 are maintained in the off state, so that the ground voltage GND is set to the P-channel MOS transistor TR-8. The voltage of the ground GND is not transmitted to the bit line Bitn via the P-channel MOS transistor TR-9.

  When precharge signal PC rises to "H" level, P-channel MOS transistors TR-3, TR-4, TR-5 are turned off. Further, when the word line WL_xxx rises to the “H” level, the N-channel MOS transistors TR-1 and TR-2 are turned on.

  When the wiring between the N channel MOS transistor TR-1 and the source line SL is not disconnected, the voltage of the ground GND on the source line SL is changed to the bit line Bit via the N channel MOS transistor TR-1. Is transmitted. As a result, the voltage of the bit line Bit decreases.

  On the other hand, since there is no program contactor between N-channel MOS transistor TR-2 and node S_xxx on source line SL, the voltage on source line SL is applied to bit via N-channel MOS transistor TR-2. Not transmitted to the line Bitn, the voltage of the bit line Bitn maintains the precharge level (vdd level).

  The differential sense amplifier 10 amplifies a minute potential difference between the bit line Bit and the bit line Bitn. As a result, the voltage of data read line CTB decreases to “L” level, and latch signal QN becomes “H” level, although not shown.

  The output latch 11 receives the “H” level latch signal QN and outputs an “L” level output signal Q.

  Here, when the wiring between the N-channel MOS transistor TR-1 and the source line SL is disconnected due to a defect in manufacturing, the voltage of the ground GND on the source line SL is changed to the N-channel MOS transistor. It is not transmitted to the bit line Bit via TR-1. As a result, as indicated by the broken line in FIG. 9, the voltage of the bit line Bit maintains the precharge level (vdd level).

  If the differential sense amplifier 10 has an offset that allows easy sensing when the bit line Bit is at the “L” level, the voltage of the data read line CTB decreases to the “L” level and is not shown. Latch signal QN is at “H” level. As a result, the output signal Q from the output latch 11 becomes the “L” level as in the case where there is no defect during manufacture. Therefore, when this semiconductor device does not have a test mode as will be described later, the shipping test is passed.

  However, both N-channel MOS transistors TR-1 and TR-2 are not connected to the source line SL, and thus may be susceptible to noise during actual operation in the market. As a result, the output signal Q from the output latch 11 becomes unstable and may become “H” level, and there is a risk of malfunction.

(First phase operation in test mode)
In the first phase, the non-conduction of the program on the bit line Bit side is detected. That is, it is detected whether there is an abnormality in the contact hole connecting the transistor connected to the bit line Bit and the source line SL among the two transistors included in the memory cell.

  FIG. 12 is a diagram illustrating a time change of a signal generated in the first phase in the test mode in the third embodiment.

  Here, focusing on the memory cell CL_xxx in FIG. 11, detection of a program abnormality of the memory cell CL_xxx in the test mode will be described.

  First, when the precharge signal PC is at the “L” level, the P-channel MOS transistors TR-3, TR-4, TR-5 are turned on, and the voltages of the bit line Bit and the bit line Bitn are set to the precharge level (vdd level). )

  When word line WL_xxx is inactive ("L" level), N-channel MOS transistors TR-1 and TR-2 are turned off, and the voltage of source line SL is not transmitted to bit line Bit and bit line Bitn. .

  Next, the precharge signal PC rises to the “H” level, the word line WL_xxx rises to the “H” level, and the switch 161 connects the source line SL to the ground GND.

  Here, the precharge circuit + CSL driver group 105 and the row decoder 103 activate the precharge signal PC and the word line WL_xxx based on the clock CLKB. Therefore, in the test mode, the period during which the precharge signal PC and the word line WL_xxx are activated has a pulse width of the clock CLKB in the test mode as shown in FIG. 5, and is longer than that in the normal mode.

  In addition, the control logic circuit 108 causes the test signal Test1 to fall to the “L” level. Test signal Test2 is maintained at the “H” level.

  When precharge signal PC rises to "H" level, P-channel MOS transistors TR-3, TR-4, TR-5 are turned off. Further, when the word line WL_xxx rises to the “H” level, the N-channel MOS transistors TR-1 and TR-2 are turned on.

  Since the test signal Test1 is at the “L” level, the P-channel MOS transistor TR-9 is turned on, and the voltage of the ground GND is transmitted to the bit line Bitn via the P-channel MOS transistor TR-9. The voltage of Bitn decreases from the ground (gnd) level to a voltage that is higher by the threshold voltage P_Vth of the P-channel MOS transistor TR-9. The voltage P_Vth is larger than the offset voltage of the differential sense amplifier 10. The test signal Test2 is always maintained at the “H” level.

  When the wiring between the N channel MOS transistor TR-1 and the source line SL is not disconnected, the voltage of the ground GND on the source line SL is changed to the bit line Bit via the N channel MOS transistor TR-1. Is transmitted. As a result, the voltage of the bit line Bit decreases.

  On the other hand, since there is no program contactor between N-channel MOS transistor TR-2 and node S_xxx on source line SL, the voltage on source line SL is applied to bit via N-channel MOS transistor TR-2. Not transmitted to the line Bitn, the voltage of the bit line Bitn maintains a voltage higher than the gnd level by the threshold voltage P_Vth of the P-channel MOS transistor TR-9.

  The differential sense amplifier 10 amplifies a minute potential difference between the bit line Bit and the bit line Bitn. As a result, the voltage of data read line CTB decreases to “L” level, and latch signal QN becomes “L” level, although not shown.

  The output latch 11 receives the “L” level latch signal QN and outputs an “L” level output signal Q.

  Here, when the wiring between the N-channel MOS transistor TR-1 and the source line SL is disconnected due to a defect in manufacturing, the voltage of the ground GND on the source line SL is changed to the N-channel MOS transistor. It is not transmitted to the bit line Bit via TR-1. As a result, as indicated by a broken line in FIG. 12, the voltage of the bit line Bit maintains the precharge level (vdd level).

  The differential sense amplifier 10 amplifies a minute potential difference between the bit line Bit and the bit line Bitn. As a result, the voltage of data read line CTB maintains the “H” level, and the latch signal QN becomes the “H” level although not shown.

  The output latch 11 receives the “H” level latch signal QN and outputs an “H” level output signal Q.

  By recognizing that the output signal Q having a level different from the normal level (expected value) is output from the output latch 11, the N-channel MOS transistor TR- 1 and the source line SL are connected to each other due to a defect in manufacturing. The wiring between them is broken, and it can be known that they are not programmed correctly.

(Second phase operation in test mode)
In the second phase, the non-conduction of the program on the bit line Bitn side is detected. That is, it is detected whether there is an abnormality in the contact hole connecting the transistor connected to the bit line Bitn and the source line SL among the two transistors included in the memory cell.

  FIG. 13 is a diagram illustrating a time change of a signal generated in the second phase in the test mode in the third embodiment.

  Here, focusing on the memory cell CL_yyy in FIG. 11, detection of a program abnormality of the memory cell CL_yyy in the test mode will be described.

  First, when the precharge signal PC is at the “L” level, the P-channel MOS transistors TR-3, TR-4, TR-5 are turned on, and the voltages of the bit line Bit and the bit line Bitn are set to the precharge level (vdd level). )

  When word line WL_yyy is inactive ("L" level), N-channel MOS transistors TR-C and TR-D are turned off, and the voltage of source line SL is not transmitted to bit line Bit and bit line Bitn. .

  Next, as the precharge signal PC rises to the “H” level, the word line WL_yyy rises to the “H” level, and the switch 161 connects the source line SL to the ground GND.

  Here, the precharge circuit + CSL driver group 105 and the row decoder 103 activate the precharge signal PC and the word line WL_yyy based on the clock CLKB. Therefore, in the test mode, the period during which the precharge signal PC and the word line WL_yyy are activated has a pulse width of the clock CLKB in the test mode as shown in FIG. 5, and is longer than that in the normal mode.

  In addition, the control logic circuit 108 causes the test signal Test2 to fall to the “L” level. Test signal Test1 is maintained at the “H” level.

  When precharge signal PC rises to "H" level, P-channel MOS transistors TR-3, TR-4, TR-5 are turned off. Further, when the word line WL_yyy rises to the “H” level, the N-channel MOS transistors TR-C and TR-D are turned on.

  Since the test signal Test2 is “L” level, the P-channel MOS transistor TR-8 is turned on, and the voltage of the ground GND is transmitted to the bit line Bit via the P-channel MOS transistor TR-8. The voltage of Bit is higher than the gnd level by the threshold voltage P_Vth of the P-channel MOS transistor TR-9. The test signal Test1 is always maintained at the “H” level.

  When the wiring between the N-channel MOS transistor TR-D and the source line SL is not disconnected, the voltage of the ground GND on the source line SL is changed to the bit line Bitn via the N-channel MOS transistor TR-D. Is transmitted. As a result, the voltage of the bit line Bitn decreases.

  On the other hand, since there is no program contactor between the N channel MOS transistor TR-C and the node S_yyy on the source line SL, the voltage on the source line SL is applied to the bit via the N channel MOS transistor TR-C. Not transmitted to the line Bit, the voltage of the bit line Bit is maintained higher than the gnd level by the threshold voltage P_Vth of the P-channel MOS transistor TR-9.

  The differential sense amplifier 10 amplifies a minute potential difference between the bit line Bit and the bit line Bitn. As a result, the voltage of data read line CTB is maintained at “H” level, and latch signal QN is set to “H” level, although not shown.

  The output latch 11 receives the “H” level latch signal QN and outputs an “H” level output signal Q.

  Here, when the wiring between the N-channel MOS transistor TR-D and the source line SL is disconnected due to a defect in manufacturing, the voltage of the ground GND on the source line SL is changed to the N-channel MOS transistor. It is not transmitted to the bit line Bit via TR-D. As a result, as indicated by a broken line in FIG. 13, the voltage of the bit line Bitn maintains the precharge level (vdd level).

  The differential sense amplifier 10 amplifies a minute potential difference between the bit line Bit and the bit line Bitn. As a result, the voltage of data read line CTB decreases to “L” level, and latch signal QN becomes “L” level, although not shown.

  The output latch 11 receives the “L” level latch signal QT and outputs an “L” level output signal Q.

  By recognizing that the output signal Q having a level different from the normal level (expected value) is output from the output latch 11, the N-channel MOS transistor TR-D and the source line SL are connected to each other due to a defect in manufacturing. The wiring between them is broken, and it can be known that they are not programmed correctly.

  As described above, according to the present embodiment, it is possible to prevent the influence of the offset voltage of the differential sense amplifier by fixing the bit line whose level is not determined to the intermediate potential in the test mode. , Test accuracy can be improved.

In the present embodiment, the circuit to be added is only the voltage fixing circuit, so that the overhead of the circuit area is small.
[Fourth Embodiment]
FIG. 14 is a diagram illustrating a partial configuration in the i-th column of the memory array 104 and the I / O circuit 107 in the fourth embodiment.

The configuration of FIG. 14 is different from the configuration of FIG. 6 as follows.
The configuration of FIG. 14 does not include the inverters IV1 and IV2 and the exclusive OR circuit EOR, but includes a voltage fixing (voltage control circuit) circuit 62 instead.

  The voltage fixing circuit 62 fixes the bit line Bit or Bitn to a voltage higher than the voltage of the ground GND and lower than the precharge voltage (vdd).

  Voltage fixing circuit 62 includes inverters IV3 and IV4 and P-channel MOS transistors TR-10 and TR-11.

  The inverter IV3 inverts the test signal Test2 and outputs a signal NTTest2.

  P-channel MOS transistor TR-10 is provided between node N_te1 on bit line Bit and power supply vdd. P channel MOS transistor TR-10 has its gate receiving signal NTest2.

  Inverter IV4 inverts test signal Test1 and outputs signal NTTest1.

  P-channel MOS transistor TR-11 is provided between node N_te2 on bit line Bitn and power supply vdd. P channel MOS transistor TR-11 has its gate receiving signal NTest1.

  The output latch 11 receives and latches the output signal QN of the differential sense amplifier 10 and outputs it as an output signal Q to the outside.

(Operation in normal mode)
The time change of the signal generated in the normal mode in the present embodiment is the same as that in the second embodiment shown in FIG. Therefore, the time change of the signal generated in the normal mode in the present embodiment will be described with reference to FIG.

  Here, paying attention to the memory cell CL_xxx in FIG. 11, the reading operation of the memory cell CL_xxx in the normal mode will be described.

  Although not shown, in the normal mode, the test signals Test 1 and Test 2 are set to “H” level by the control logic circuit 108.

  First, when the precharge signals PC0, PC1, and PC2 are at "L" level, the P-channel MOS transistors TR-3, TR-4, and TR-5 are turned on, and the voltages of the bit line Bit and the bit line Bitn are at the precharge level. (Vdd level).

  When word line WL_xxx is inactive ("L" level), N-channel MOS transistors TR-1 and TR-2 are turned off, and the voltage of source line SL is not transmitted to bit line Bit and bit line Bitn. .

  Next, the precharge signals PC0, PC1, and PC2 rise to the “H” level, the word line WL_xxx rises to the “H” level, and the switch 161 connects the source line SL to the ground GND.

  Here, the precharge circuit + CSL driver group 105 and the row decoder 103 activate the precharge signal PC and the word line WL_xxx based on the clock CLKB. Therefore, in the normal mode, the period during which the precharge signal PC and the word line WL_xxx are activated has the pulse width of the clock CLKB in the normal mode as shown in FIG. 4, and is shorter than in the test mode.

  In the normal mode, since the test signals Test1 and Test2 are at “H” level, the N-channel MOS transistors TR-10 and TR-11 are maintained in the off state, so that the power supply voltage vdd The power supply voltage vdd is not transmitted to the bit line Bitn via the N-channel MOS transistor TR-11.

  When precharge signals PC0, PC1, and PC2 rise to "H" level, P channel MOS transistors TR-3, TR-4, and TR-5 are turned off. Since P-channel MOS transistor TR-5 is off, equalization between bit line Bit and bit line Bitn is not performed.

  Further, when the word line WL_xxx rises to the “H” level, the N-channel MOS transistors TR-1 and TR-2 are turned on.

  When the wiring between the N channel MOS transistor TR-1 and the source line SL is not disconnected, the voltage of the ground GND on the source line SL is changed to the bit line Bit via the N channel MOS transistor TR-1. Is transmitted. As a result, the voltage of the bit line Bit decreases.

  On the other hand, since there is no program contactor between N-channel MOS transistor TR-2 and node S_xxx on source line SL, the voltage on source line SL is applied to bit via N-channel MOS transistor TR-2. Not transmitted to the line Bitn, the voltage of the bit line Bitn maintains the precharge level (vdd level).

  The differential sense amplifier 10 amplifies a minute potential difference between the bit line Bit and the bit line Bitn. As a result, the voltage of data read line CTB decreases to “L” level, and latch signal QN becomes “L” level, although not shown.

  The output latch 11 receives the “L” level latch signal QN and outputs an “L” level output signal Q.

  Here, when the wiring between the N-channel MOS transistor TR-1 and the source line SL is disconnected due to a defect in manufacturing, the voltage of the ground GND on the source line SL is changed to the N-channel MOS transistor. It is not transmitted to the bit line Bit via TR-1. As a result, as indicated by the broken line in FIG. 9, the voltage of the bit line Bit maintains the “H” level (vdd level).

  If the differential sense amplifier 10 has an offset that allows easy sensing when the bit line Bit is at the “L” level, the voltage of the data read line CTB decreases to the “L” level and is not shown. Latch signal QN is at “H” level. As a result, the output signal Q from the output latch 11 becomes the “L” level as in the case where there is no defect during manufacture. Therefore, when this semiconductor device does not have a test mode as will be described later, the shipping test is passed.

  However, both N-channel MOS transistors TR-1 and TR-2 are not connected to the source line SL, and thus may be susceptible to noise during actual operation in the market. As a result, the output signal Q from the output latch 11 becomes unstable and may become “H” level, and there is a risk of malfunction.

(First phase operation in test mode)
In the first phase, the non-conduction of the program on the bit line Bit side is detected. That is, it is detected whether there is an abnormality in the contact hole connecting the transistor connected to the bit line Bit and the source line SL among the two transistors included in the memory cell.

  FIG. 15 is a diagram illustrating a time change of a signal generated in the first phase in the test mode in the fourth embodiment.

  Here, focusing on the memory cell CL_xxx in FIG. 14, detection of a program abnormality of the memory cell CL_xxx in the test mode will be described.

  In the initial state, the precharge signals PC0 and PC2 and the test signal Test2 are set to the “H” level, the precharge signal PC1 and the test signal Test1 are set to the “L” level, and the word line WL_xxx is inactivated (“L” level). Become.

  At this time, P-channel MOS transistors TR-4 and TR-5 are turned off, P-channel MOS transistor TR-3 is turned on, N-channel MOS transistor TR-10 is turned off, and N-channel MOS transistor TR-11 is turned on.

  As a result, the voltage of the bit line Bit becomes the precharge level (vdd level). Further, the voltage of the bit line Bitn becomes a voltage lower than the precharge level (vdd level) by the threshold voltage N_Vth of the N-channel MOS transistor TR-11. The voltage N_Vth is larger than the offset voltage of the differential sense amplifier 10.

  At this time, the N-channel MOS transistors TR-1 and TR-2 are turned off.

  As a result, the voltage of the source line SL is not transmitted to the bit line Bit and the bit line Bitn.

  Next, the precharge circuit + CSL driver group 105 and the row decoder 103 activate the precharge signal PC1 and the word line WL_xxx based on the clock CLKB. Therefore, in the test mode, the period during which the precharge signal PC1 and the word line WL_xxx are activated has a pulse width of the clock CLKB in the test mode as shown in FIG. 5, and is longer than that in the normal mode.

  Further, the source line SL is connected to the ground GND by the switch 161, and the test signal Test 1 rises to “H” level by the control logic circuit 108.

  As precharge signal PC1 rises to "H" level, P channel MOS transistor TR-3 is turned off. When test signal Test1 rises to "H" level, N-channel MOS transistor TR-11 is turned off.

  As a result, when the wiring between the N channel MOS transistor TR-1 and the source line SL is not disconnected, the voltage of the ground GND on the source line SL passes through the N channel MOS transistor TR-1. It is transmitted to the bit line Bit. As a result, the voltage of the bit line Bit decreases.

  On the other hand, since there is no program contactor between N-channel MOS transistor TR-2 and node S_xxx on source line SL, the voltage on source line SL is applied to bit via N-channel MOS transistor TR-2. Without being transmitted to the line Bitn, the voltage of the bit line Bitn is maintained at a voltage lower than the precharge level (vdd level) by N_Vth.

  The differential sense amplifier 10 amplifies a minute potential difference between the bit line Bit and the bit line Bitn. As a result, although not shown, the voltage of data read line CTB is reduced to “L” level and latch signal QN is set to “L” level.

  The output latch 11 receives the “L” level latch signal QN and outputs an “L” level output signal Q.

  Here, when the wiring between the N-channel MOS transistor TR-1 and the source line SL is disconnected due to a defect in manufacturing, the voltage of the ground GND on the source line SL is changed to the N-channel MOS transistor. It is not transmitted to the bit line Bit via TR-1. As a result, as indicated by a broken line in FIG. 15, the voltage of the bit line Bit maintains the precharge level (vdd level).

  The differential sense amplifier 10 amplifies a minute potential difference between the bit line Bit and the bit line Bitn. As a result, the voltage on data read line CTB maintains the precharge level (vdd level), and latch signal QN attains the “H” level.

  The output latch 11 receives the “H” level latch signal QT and outputs an “H” level output signal Q.

  By recognizing that the output signal Q having a level different from the normal level (expected value) is output from the output latch 11, the N-channel MOS transistor TR- 1 and the source line SL are connected to each other due to a defect in manufacturing. The wiring between them is broken, and it can be known that they are not programmed correctly.

(Second phase operation in test mode)
In the second phase, the non-conduction of the program on the bit line Bitn side is detected. That is, it is detected whether there is an abnormality in the contact hole connecting the transistor connected to the bit line Bitn and the source line SL among the two transistors included in the memory cell.

  FIG. 16 is a diagram illustrating a time change of a signal generated in the second phase in the test mode in the fourth embodiment.

  Here, focusing on the memory cell CL_yyy in FIG. 14, detection of a program abnormality of the memory cell CL_yyy in the test mode will be described.

  In the initial state, the precharge signals PC0 and PC1 and the test signal Test1 are set to “H” level, the precharge signal PC2 and the test signal Test2 are set to “L” level, and the word line WL_yyy is inactivated (“L” level). Become.

  At this time, P channel MOS transistors TR-3 and TR-5 are turned off, P channel MOS transistor TR-4 is turned on, N channel MOS transistor TR-11 is turned off, and N channel MOS transistor TR-10 is turned on.

  As a result, the voltage of the bit line Bitn becomes the precharge level (vdd level). Further, the voltage of the bit line Bit becomes a voltage lower than the precharge level (vdd level) by the threshold voltage N_Vth of the N-channel MOS transistor TR-10. The voltage N_Vth is larger than the offset voltage of the differential sense amplifier 10.

  At this time, the N-channel MOS transistors TR-C and TR-D are turned off.

  As a result, the voltage of the source line SL is not transmitted to the bit line Bit and the bit line Bitn.

  Next, the precharge circuit + CSL driver group 105 and the row decoder 103 activate the precharge signal PC2 and the word line WL_yyy based on the clock CLKB. Therefore, in the test mode, the period in which the precharge signal PC2 and the word line WL_yyy are activated has a pulse width of the clock CLKB in the test mode as shown in FIG. 5, and is longer than that in the normal mode.

  Further, the source line SL is connected to the ground GND by the switch 161, and the test signal Test 2 rises to the “H” level by the control logic circuit 108.

  When precharge signal PC2 rises to "H" level, P channel MOS transistor TR-4 is turned off. When test signal Test2 rises to "H" level, N-channel MOS transistor TR-10 is turned off.

  As a result, when the wiring between the N channel MOS transistor TR-D and the source line SL is not disconnected, the voltage of the ground GND on the source line SL passes through the N channel MOS transistor TR-D. It is transmitted to the bit line Bitn. As a result, the voltage of the bit line Bitn decreases.

  On the other hand, since there is no program contactor between the N channel MOS transistor TR-C and the node S_xxx on the source line SL, the voltage on the source line SL is applied to the bit via the N channel MOS transistor TR-C. Without being transmitted to the line Bit, the voltage of the bit line Bit is maintained at a voltage lower by N_Vth than the precharge level (vdd level).

  The differential sense amplifier 10 amplifies a minute potential difference between the bit line Bit and the bit line Bitn. As a result, the voltage of data read line CTB is maintained at “H” level, and latch signal QN is at “H” level.

  The output latch 11 receives the “H” level latch signal QN and outputs an “H” level output signal Q.

  Here, when the wiring between the N-channel MOS transistor TR-D and the source line SL is disconnected due to a defect in manufacturing, the voltage of the ground GND on the source line SL is changed to the N-channel MOS transistor. Not transmitted to the bit line Bitn via TR-D. As a result, as indicated by a broken line in FIG. 16, the voltage of the bit line Bitn maintains the precharge level (vdd level).

  The differential sense amplifier 10 amplifies a minute potential difference between the bit line Bit and the bit line Bitn. As a result, the voltage of data read line CTB decreases to “L” level, and latch signal QN becomes “L” level.

  The output latch 11 receives the “L” level latch signal QT and outputs an “L” level output signal Q.

  By recognizing that the output signal Q having a level different from the normal level (expected value) is output from the output latch 11, the N-channel MOS transistor TR- 1 and the source line SL are connected to each other due to a defect in manufacturing. The wiring between them is broken, and it can be known that they are not programmed correctly.

  As described above, according to the present embodiment, as in the third embodiment, the offset voltage of the differential sense amplifier is fixed by fixing the bit line whose level is not determined to the intermediate potential in the test mode. Therefore, it is possible to improve the accuracy of the test.

In the present embodiment, the circuit to be added is only the voltage fixing circuit, so that the overhead of the circuit area is small.
[Fifth Embodiment]
FIG. 17 is a diagram illustrating a partial configuration in the i-th column of the memory array 104 and the I / O circuit 107 in the fifth embodiment.

The configuration of FIG. 17 is different from the configuration of FIG. 6 as follows.
The configuration of FIG. 17 does not include the inverters IV1 and IV2 and the exclusive OR circuit EOR, but includes a short circuit 63 instead.

  The short circuit 63 short-circuits the bit line Bit and the bit line Bitn in the test mode.

Short circuit 63 includes P-channel MOS transistor TR-12.
P-channel MOS transistor TR-12 is provided between node N_te1 on bit line Bit and node N_te2 on bit line Bitn. The gate of P channel MOS transistor TR-12 receives test signal Test.

  The output latch 11 receives and latches the output signal QN of the differential sense amplifier 10 and outputs it as an output signal Q to the outside.

(Operation in normal mode)
The time change of the signal generated in the normal mode in the present embodiment is the same as that in the second embodiment shown in FIG. Therefore, the time change of the signal generated in the normal mode in the present embodiment will be described with reference to FIG.

  Here, paying attention to the memory cell CL_xxx in FIG. 17, the read operation of the memory cell CL_xxx in the normal mode will be described.

  Referring to FIG. 9, first, when precharge signal PC is at "L" level, P channel MOS transistors TR-3, TR-4, TR-5 are turned on, and the voltages of bit line Bit and bit line Bitn are turned on. It becomes a precharge level (vdd level).

  When word line WL_xxx is inactive ("L" level), N-channel MOS transistors TR-1 and TR-2 are turned off, and the voltage of source line SL is not transmitted to bit line Bit and bit line Bitn. .

  Next, the precharge signal PC rises to the “H” level, the word line WL_xxx rises to the “H” level, and the switch 161 connects the source line SL to the ground GND.

  Here, the precharge circuit + CSL driver group 105 and the row decoder 103 activate the precharge signal PC and the word line WL_xxx based on the clock CLKB. Therefore, in the normal mode, the period during which the precharge signal PC and the word line WL_xxx are activated has the pulse width of the clock CLKB in the normal mode as shown in FIG. 4, and is shorter than in the test mode.

  In the normal mode, since the test signal Test is at “L” level, the N-channel MOS transistor TR-12 maintains the OFF state, and the bit line Bit and the bit line Bitn are connected via the N-channel MOS transistor TR-12. There is no connection.

  When precharge signal PC rises to "H" level, P-channel MOS transistors TR-3, TR-4, TR-5 are turned off. Further, when the word line WL_xxx rises to the “H” level, the N-channel MOS transistors TR-1 and TR-2 are turned on.

  When the wiring between the N channel MOS transistor TR-1 and the source line SL is not disconnected, the voltage of the ground GND on the source line SL is changed to the bit line Bit via the N channel MOS transistor TR-1. Is transmitted. As a result, the voltage of the bit line Bit decreases.

  On the other hand, since there is no program contactor between N-channel MOS transistor TR-2 and node S_xxx on source line SL, the voltage on source line SL is applied to bit via N-channel MOS transistor TR-2. Not transmitted to the line Bitn, the voltage of the bit line Bitn maintains the precharge level (vdd level).

  The differential sense amplifier 10 amplifies a minute potential difference between the bit line Bit and the bit line Bitn. As a result, the voltage of data read line CTB decreases to “L” level, and latch signal QN becomes “L” level, although not shown.

  The output latch 11 receives the “L” level latch signal QN and outputs an “L” level output signal Q.

  Here, when the wiring between the N-channel MOS transistor TR-1 and the source line SL is disconnected due to a defect in manufacturing, the voltage of the ground GND on the source line SL is changed to the N-channel MOS transistor. It is not transmitted to the bit line Bit via TR-1. As a result, as indicated by the broken line in FIG. 9, the voltage of the bit line Bit maintains the precharge level (vdd level).

  If the differential sense amplifier 10 has an offset that allows easy sensing when the bit line Bit is at the “L” level, the voltage of the data read line CTB decreases to the “L” level and is not shown. Latch signal QN is at “H” level. As a result, the output signal Q from the output latch 11 becomes the “L” level as in the case where there is no defect during manufacture. Therefore, when this semiconductor device does not have a test mode as will be described later, the shipping test is passed.

  However, both N-channel MOS transistors TR-1 and TR-2 are not connected to the source line SL, and thus may be susceptible to noise during actual operation in the market. As a result, the output signal Q from the output latch 11 becomes unstable and may become “H” level, and there is a risk of malfunction.

(Operation in test mode)
FIG. 18 is a diagram illustrating a time change of a signal generated in the test mode in the fifth embodiment.

  Here, focusing on the memory cell CL_xxx in FIG. 17, detection of a program abnormality of the memory cell CL_xxx in the test mode will be described.

  First, when the precharge signal PC is at the “L” level, the P-channel MOS transistors TR-3, TR-4, TR-5 are turned on, and the voltages of the bit line Bit and the bit line Bitn are at the precharge level (vdd level). It becomes.

  When word line WL_xxx is inactive ("L" level), N-channel MOS transistors TR-1 and TR-2 are turned off, and the voltage of source line SL is not transmitted to bit line Bit and bit line Bitn. .

  Next, the precharge signal PC rises to the “H” level, the word line WL_xxx rises to the “H” level, and the switch 161 connects the source line SL to the ground GND.

  Here, the precharge circuit + CSL driver group 105 and the row decoder 103 activate the precharge signal PC and the word line WL_xxx based on the clock CLKB. Therefore, in the test mode, the period during which the precharge signal PC and the word line WL_xxx are activated has a pulse width of the clock CLKB in the test mode as shown in FIG. 5, and is longer than that in the normal mode.

  In the test mode, the control signal 108 is set to the “H” level by the control logic circuit 108.

  When precharge signal PC rises to "H" level, P-channel MOS transistors TR-3, TR-4, TR-5 are turned off. Further, when the word line WL_xxx rises to the “H” level, the N-channel MOS transistors TR-1 and TR-2 are turned on.

  Since test signal Test is at “H” level, N-channel MOS transistor TR-12 is turned on, and bit line Bit and bit line Bitn are connected via N-channel MOS transistor TR-12.

  When the wiring between the N channel MOS transistor TR-1 and the source line SL is not disconnected, the voltage of the ground GND on the source line SL is changed to the bit line Bit via the N channel MOS transistor TR-1. Is transmitted. As a result, the voltage of the bit line Bit gradually decreases.

  On the other hand, since there is no program contactor between N-channel MOS transistor TR-2 and node S_xxx on source line SL, the voltage on source line SL is applied to bit via N-channel MOS transistor TR-2. Not transmitted on line Bitn. However, since the N-channel MOS transistor TR-12 is in the on state, the voltage of the bit line Bit is transmitted to the bit line Bitn, and the voltage of the bit line Bit gradually decreases in the same manner as the voltage of the bit line Bit. .

  At this time, in the present embodiment, unlike the other embodiments, the sense amplifier activation signal SAE is not activated to the “H” level, and the differential sense amplifier 10 is not activated. As a result, the voltage of data read line CTB decreases to “L” level, which is the voltage of bit line Bit, and latch signal QN becomes “L” level.

  The output latch 11 receives the “L” level latch signal QN and outputs an “L” level output signal Q.

  Here, when the wiring between the N-channel MOS transistor TR-1 and the source line SL is disconnected due to a defect in manufacturing, the voltage of the ground GND on the source line SL is changed to the N-channel MOS transistor. It is not transmitted to the bit line Bit via TR-1. As a result, as indicated by a broken line in FIG. 18, the voltage of the bit line Bit maintains the precharge level (vdd level). Further, since the N-channel MOS transistor TR-12 is in the ON state, the voltage of the bit line Bit is transmitted to the bit line Bitn, and the voltage of the bit line Bit is the same as the voltage of the bit line Bit. vdd level). At this time, in the present embodiment, unlike the other embodiments, the sense amplifier activation signal SAE is not activated to the “H” level, and the differential sense amplifier 10 is not activated. As a result, the voltage of data read line CTB maintains the “H” level that is the voltage of bit line Bit, and latch signal QN attains the “H” level.

  The output latch 11 receives the “H” level latch signal QN and outputs an “H” level output signal Q.

  By recognizing that the output signal Q having a level different from the normal level (expected value) is output from the output latch 11, the N-channel MOS transistor TR- 1 and the source line SL are connected to each other due to a defect in manufacturing. The wiring between them is broken, and it can be known that they are not programmed correctly.

  As described above, according to the present embodiment, in the test mode, the bit line pair is short-circuited and the level of the bit line pair is determined without operating the differential sense amplifier. Therefore, the accuracy of the test can be improved.

  Moreover, since the expected value in the test mode does not depend on the program code, BIST (Built-In Self-Test) is facilitated.

  In the present embodiment, the circuit to be added is only a short circuit, so that the circuit area overhead is small.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

  50 precharge circuit, 51, 52, 55, IV1, IV2, IV3, IV4, IV11 inverter, 53, 54 NAND circuit, 56 delay circuit, 58, 220 column selector, 61, 62 voltage fixing circuit, 63 short circuit 10, 503 differential sense amplifier, 11, 504 output latch, 101 address predecoder, 102 control circuit, 103 row decoder, 104 memory array, 105 precharge circuit + SL driver group, 106 column selector group, 107 I / O circuit , 108 control logic circuit, 110-1 to 110-5, 110-a latch, 111-1 to 111-5 predecoder, 112 internal clock generation circuit, 210 differential sense amplifier group, 211 output latch group, 161 switch 230 Amplifier 220 Charge and equalizing unit, 240 buffer, 245,505 logic circuits, TR-1, TR-2, TR-A, TR-B, TR-C ,. TR-D, TR-10, TR-11, TR-12, N1-N3, N5 N-channel MOS transistors, TR-3, TR-4, TR-5, TR-6, TR-7, TR-8, TR-9, P3-P8, P10 P-channel MOS transistor, EOR exclusive OR circuit, MUX multiplexer, CL, CL_000, CL_xxx, CL_yyy memory cell, WL, WL_000, WL_xxx, WL_yyy Word line, SL source line, Bit, Bitn bit line.

Claims (11)

A plurality of memory cells;
A word line connected to the plurality of memory cells;
A first bit line and a second bit line connected to the plurality of memory cells;
A differential sense amplifier for amplifying a potential difference between the first and second bit lines;
A semiconductor device comprising a voltage control circuit for controlling at least one of the first and second bit lines to a voltage higher than a ground voltage and lower than a precharge voltage in the first mode. .   The semiconductor device according to claim 1, further comprising: a decoder that activates a word line in the first mode for a longer period than in the second mode.   When the voltage control circuit detects a failure of the memory cell on the first bit line side among the plurality of memory cells in the first mode, the voltage control circuit sets the voltage of the second bit line to the ground. A voltage higher than the voltage and lower than the precharge voltage, and when detecting a failure of the memory cell on the second bit line side among the plurality of memory cells, The semiconductor device according to claim 2, wherein the voltage is controlled to be higher than the ground voltage and lower than the precharge voltage. The voltage control circuit includes:
A first P-channel MOS transistor provided between the first bit line and the ground;
4. The semiconductor device according to claim 3, comprising a second P-channel MOS transistor provided between the second bit line and the ground. The gate of the second P-channel MOS transistor receives the first signal,
The gate of the first P-channel MOS transistor receives a second signal,
5. The semiconductor device according to claim 4, further comprising: a control logic circuit that sets the first signal and the second signal to a low level during a period in which the word line is activated in the first mode. The voltage control circuit includes:
A first N-channel MOS transistor provided between the first bit line and a power supply voltage;
4. The semiconductor device according to claim 3, further comprising a second N channel MOS transistor provided between the second bit line and a power supply voltage. The gate of the second N-channel MOS transistor receives the first signal,
A gate of the first N-channel MOS transistor receives a second signal;
The semiconductor device according to claim 6, further comprising: a control logic circuit that sets the first signal and the second signal to a low level during a period in which the word line is activated in the first mode. A plurality of memory cells;
A word line connected to the plurality of memory cells;
A first bit line and a second bit line connected to the plurality of memory cells;
A differential sense amplifier for amplifying a potential difference between the first and second bit lines;
A semiconductor device comprising a short circuit for short-circuiting the first bit line and the second bit line.   9. The semiconductor device according to claim 8, further comprising: a decoder that activates the word line in the first mode for a longer time than in the second mode.   The semiconductor device according to claim 9, wherein the short circuit includes an N-channel MOS transistor provided between the first bit line and the second bit line.   11. The semiconductor device according to claim 10, further comprising: a control logic circuit that sets a signal received at a gate of the N-channel MOS transistor to a high level during a period in which the word line is activated in the first mode.

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