Abstract:
A cut-off circuit cuts off supply of a power supply voltage from a voltage supply circuit to a non-volatile memory block. A discharge circuit discharges an electric charge accumulated in stability capacitance. In a data retention test of the memory block, a self test circuit instructs the cut-off circuit to start operation after writing predetermined data into the memory block, and instructs the cut-off circuit to stop the operation to check retention of the predetermined data in the memory block in a predetermined time after the instruction to the cut-off circuit to start the operation. Further, in the data retention test of the memory block, the self test circuit instructs the discharge circuit to start operation along with the instruction to the cut-off circuit to start the operation, and instructs the discharge circuit to stop the operation along with the instruction to the cut-off circuit to stop the operation.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2006-238119, filed on Sep. 1, 2006, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a semiconductor device, and particularly relates to a semiconductor device incorporating a non-volatile semiconductor memory (such as a ferroelectric memory). 
     2. Description of the Related Art 
     Generally, in a semiconductor device incorporating a ferroelectric memory, a voltage supplied via an external power supply pin or a voltage obtained by boosting/stepping down the voltage supplied via the external power supply pin is used as a power supply voltage of the ferroelectric memory. Among the semiconductor devices each incorporating the ferroelectric memory, in an IC card (Integrated Circuit Card), a RFID (Radio Frequency Identification), and so on, a stability capacitance (constituted of a ferroelectric capacitance) is often connected between a power supply pin of the ferroelectric memory and a ground line in order to stabilize the power supply voltage of the ferroelectric memory. 
     The ferroelectric memory has a failure mode regarding data retention called a retention failure, and hence it needs to be guaranteed to retain write data for a predetermined time or more in a power-on state (state in which the power supply voltage is being supplied) and retain write data for a predetermined time or more in a power-off state (state in which the power supply voltage is not being supplied). 
     Therefore, in a test process of the semiconductor device incorporating the ferroelectric memory, a screening test for a retention failure when the ferroelectric memory is powered off (power-off retention test) is performed in the following steps. First, predetermined data is written into the ferroelectric memory. Subsequently, the voltage supply from an external testing apparatus to an external power supply pin of the semiconductor device is stopped to stop the supply of the power supply voltage to the ferroelectric memory. Then, in a predetermined time after the supply of the power supply voltage to the ferroelectric memory is stopped, the voltage supply from the external testing apparatus to the external power supply pin of the semiconductor device is resumed to resume the supply of the power supply voltage to the ferroelectric memory. Thereafter, data is read from the ferroelectric memory, and the presence or absence of the retention failure is determined by comparing the read data and the predetermined data. 
     Moreover, Japanese Unexamined Patent Application Publication No. 2000-299000 discloses a non-volatile semiconductor memory which is configured to be able to supply a voltage obtained by stepping down a power supply voltage to a memory block in addition to the power supply voltage and to ensure reliable data retention even when the memory block is constituted of a ferroelectric memory. Japanese Unexamined Patent Application Publication No. 2004-61114 discloses a self-diagnosis test circuit which can realize a reduction in test time, an improvement in yield, and an increase in test coverage in a test of a semiconductor device. 
     In the conventional semiconductor device, to stop the supply of the power supply voltage to the ferroelectric memory in the power-off retention test of the ferroelectric memory, the supply of the voltage from the external testing apparatus to the external power supply pin of the semiconductor device needs to be stopped. Therefore, during the power-off retention test of the ferroelectric memory, the supply of the power supply voltage to functional blocks except the ferroelectric memory is also stopped. This causes a problem that during the power-off retention test of the ferroelectric memory, the functional blocks except the memory block cannot be tested, thereby increasing a test time of the semiconductor device. 
     Further, with the stability capacitance, even if the voltage supply from the external testing apparatus to the external power supply pin of the semiconductor device is stopped to stop the supply of the power supply voltage to the ferroelectric memory in the power-off retention test thereof, the voltage is supplied to the ferroelectric memory only for a time taken for discharging an electric charge accumulated in the stability capacitance. Hence, whit the stability capacitance, it is necessary to lengthen the time for stopping of the voltage supply from the external testing apparatus to the external power supply pin of the semiconductor device by the waiting time for the completion of discharge of the electric charge accumulated in the stability capacitance, which causes a problem of an increase in the test time of the semiconductor device. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to reduce a test time of a semiconductor device incorporating a non-volatile semiconductor memory. 
     In a first aspect of the present invention, a semiconductor device includes plural functional blocks, a voltage supply circuit, a cut-off circuit, and a self test circuit. The plural functional blocks include a non-volatile memory block. For example, the memory block is constituted of a ferroelectric memory. The voltage supply circuit supplies a power supply voltage to the functional blocks. The cut-off circuit cuts off the supply of the power supply voltage from the voltage supply circuit to the memory block. The self test circuit performs tests of the functional blocks. In a data retention test of the memory block, the self test circuit instructs the cut-off circuit to start an operation after writing predetermined data into the memory block, and instructs the cut-off circuit to stop the operation to check retention of the predetermined data in the memory block in a predetermined time after the instruction to the cut-off circuit to start the operation. 
     For example, the semiconductor device further includes a stability capacitance and a discharge circuit. The stability capacitance is connected between a power supply pin of the memory block and a ground line. For example, the stability capacitance is constituted of a ferroelectric capacitance. The discharge circuit discharges an electric charge accumulated in the stability capacitance. In the data retention test of the memory block, the self test circuit instructs the discharge circuit to start an operation along with the instruction to the cut-off circuit to start the operation, and instructs the discharge circuit to stop the operation along with the instruction to the cut-off circuit to stop the operation. 
     In the above first aspect, in the data retention test of the memory block by the self test circuit, the supply of the power supply voltage from the voltage supply circuit to the memory block is cut off, but the supply of the power supply voltage from the voltage supply circuit to the functional blocks except the memory block is not cut off. Hence, the self test circuit can perform tests of the functional blocks except the memory block in parallel with performing the data retention test of the memory block. 
     Further, in the data retention test of the memory block by the self test circuit, the electric charge accumulated in the stability capacitance is discharged along with cut off of the supply of the power supply voltage from the voltage supply circuit to the memory block. Therefore, in the data retention test of the memory block by the self test circuit, the time taken for cutting off the supply of the power supply voltage from the power supply circuit to the memory block does not need to include waiting time for the completion of discharge of the electric charge accumulated in the stability capacitance. In the first aspect described above, the test time of the semiconductor device can be greatly reduced, which contributes to cost reduction. 
     In a preferred example of the first aspect of the present invention, the cut-off circuit includes a voltage supply control switch. The voltage supply control switch is connected between a power supply line and the power supply pin of the memory block, the power supply line being supplied with the power supply voltage by the voltage supply circuit. The voltage supply control switch is turned off in response to the instruction from the self test circuit to the cut-off circuit to start the operation, and turned on in response to the instruction from the self test circuit to the cut-off circuit to stop the operation. Consequently, the cut-off circuit which cuts off the supply of the power supply voltage from the voltage supply circuit to the memory block can be easily constituted. 
     In a preferred example of the first aspect of the present invention, the discharge circuit includes a discharge control switch. The discharge control switch is connected between the power supply pin of the memory block and the ground line. The discharge control switch is turned on in response to the instruction from the self test circuit to the discharge circuit to start the operation, and turned off in response to the instruction from the self test circuit to the discharge circuit to stop the operation. Consequently, the discharge circuit which discharges the electric charge accumulated in the stability capacitance can be easily constituted. 
     In a second aspect of the present invention, a semiconductor device includes plural functional blocks, a voltage supply circuit, a cut-off circuit, and a self test circuit. The plural functional blocks include a non-volatile memory block. The voltage supply circuit supplies a first power supply voltage to the memory block and supplies a second power supply voltage to at least one of the functional blocks except the memory block. For example, the voltage supply circuit includes first and second voltage generating circuits. The first voltage generating circuit generates the first power supply voltage using an external input voltage, and the second voltage generating circuit generates the second power supply voltage by stepping down the first power supply voltage. Alternatively, the first voltage generating circuit generates the second power supply voltage using the external input voltage, and the second voltage generating circuit generates the first power supply voltage by boosting the second power supply voltage. The cut-off circuit cuts off the supply of the first power supply voltage from the voltage supply circuit to the memory block. The self test circuit performs tests of the functional blocks. In a data retention test of the memory block, the self test circuit instructs the cut-off circuit to start an operation after writing predetermined data into the memory block, and instructs the cut-off circuit to stop the operation to check retention of the predetermined data in the memory block in a predetermined time after the instruction to the cut-off circuit to start the operation. 
     For example, the semiconductor device further includes a stability capacitance and a discharge circuit. The stability capacitance is connected between a power supply pin of the memory block and a ground line. The discharge circuit discharges an electric charge accumulated in the stability capacitance. In the data retention test of the memory block, the self test circuit instructs the discharge circuit to start an operation along with the instruction to the cut-off circuit to start the operation, and instructs the discharge circuit to stop the operation along with the instruction to the cut-off circuit to stop the operation. 
     The above second aspect can obtain the same effect as the above first aspect, although in the second aspect an operation voltage of the memory block is different from an operation voltage of at least one of the functional blocks except the memory block, and the semiconductor device has two separate internal power supply systems; one with the first power supply voltage and the other with the second power supply voltage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The nature, principle, and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by identical reference numbers, in which: 
         FIG. 1  is a block diagram showing a first embodiment of the present invention; 
         FIG. 2  is a flowchart showing the operation of a BIST circuit in the first embodiment; 
         FIG. 3  is a block diagram showing a second embodiment of the present invention; and 
         FIG. 4  is a block diagram showing a third embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Embodiments of the present invention will be described below using the drawings. 
       FIG. 1  shows a first embodiment of the present invention. A semiconductor device  10  of the first embodiment includes a power supply circuit  11 , a logic block  13 , a memory block  14 , a BIST (Built-In Self Test) circuit  15 , a voltage supply control switch  16 , a stability capacitance  17 , and a discharge control switch  18 . The power supply circuit  11  generates a power supply voltage VDD 1  using an external input voltage VDD (voltage supplied from outside via a power supply pin PE) and supplies the power supply voltage VDD 1  to a power supply line PL 1 . 
     The logic block  13  embodies a processor function, a timer function, a communication interface function, and so on. The logic block  13  can perform a read access and a write access to the memory block  14 . The memory block  14  is constituted of a ferroelectric memory including plural memory cells (each constituted of a ferroelectric capacitance and a transfer transistor) arranged in a matrix. In the memory block  14 , the ferroelectric capacitance and the transfer transistor which constitute the memory cell are connected in series between a plate line and a bit line, and a gate of the transfer transistor is connected to a word line. 
     The BIST circuit  15  performs various tests of the logic block  13  and the memory block  14  (an operation test of the logic block  13 , an operation test of the memory block  14 , a power-on retention test/power-off retention test of the memory block  14 , and so on). The BIST circuit  15  performs on/off control of the voltage supply control switch  16  and the discharge control switch  18  when performing the power-off retention test of the memory block  14 . Details of this operation will be described later using  FIG. 2 . 
     The voltage supply control switch  16  is provided to cut off the supply of the power supply voltage VDD 1  from the power supply circuit  11  to a power supply pin PM of the memory block  14  and connected between the power supply line PL 1  and a power supply line PL 1   a  (power supply pin PM of the memory block  14 ). The power supply control switch  16  is turned on/off in response to an instruction of the BIST circuit  15 . The stability capacitance  17  is provided to stabilize a voltage (voltage of the power supply line PL 1   a ) supplied to the power supply pin PM of the memory block  14  and connected between the power supply line PL 1   a  (power supply pin PM of the memory block  14 ) and a ground line GL. The stability capacitance  17  is constituted of a ferroelectric capacitance. The discharge control switch  18  is provided to discharge an electric charge accumulated in the stability capacitance  17  and connected between the power supply line PL 1   a  (power supply pin PM of the memory block  14 ) and the ground line GL. The discharge control switch  18  is turned on/off in response to an instruction of the BIST circuit  15 . 
       FIG. 2  shows the operation of the BIST circuit in the first embodiment. When performing the power-off retention test of the memory block  14 , the BIST circuit  15  operates as follows. First, the BIST circuit  15  writes predetermined data into the memory block  14  (step S 11 ). Then, the BIST circuit  15  gives an instruction to turn off the voltage supply control switch  16  (step S 12 ). Consequently, the voltage supply control switch  16  is turned off, the power supply line PL 1  and the power supply line PL 1   a  are disconnected, and the supply of the power supply voltage VDD 1  from the power supply circuit  11  to the memory block  14  is cut off. Subsequently, the BIST circuit  15  gives an instruction to turn on the discharge control switch  18  (step S 13 ). Consequently, the discharge control switch  18  is turned on, and the electric charge accumulated in the stability capacitance  17  is immediately discharged to the ground line GL. 
     Then, in a predetermined time T after the instruction to turn on the discharge control switch  18  is given, the BIST circuit  15  gives an instruction to turn off the discharge control switch  18  (step S 14 ). Hence, the discharge control switch  18  is turned off. Subsequently, the BIST circuit  15  gives an instruction to turn on the voltage supply control switch  16  (step S 15 ). Consequently, the voltage supply control switch  16  is turned on, the power supply line PL 1  and the power supply line PL 1   a  are connected, and the supply of the power supply voltage VDD 1  from the power supply circuit  11  to the memory block  14  is resumed. After this, the BIST circuit  15  checks retention of the predetermined data in the memory block  14  (step S 16 ). To put it in more detail, after reading data from the memory block  14 , the BIST circuit  15  determines the presence or absence of a retention failure by a comparison between the read data and the predetermined data (data written into the memory block  14  in step S 11 ). 
     In the above first embodiment, when the BIST circuit  15  performs the power-off retention test of the memory block  14 , the supply of the power supply voltage VDD 1  from the power supply circuit  11  to the memory block  14  is cut off, but the supply of the power supply voltage VDD 1  from the power supply circuit  11  to the logic block  13  is not cut off. Hence, the BIST circuit  15  can perform an operation test of the logic block  13  in parallel with performing the power-off retention test of the memory block  14 . 
     Further, when the BIST circuit  15  performs the power-off retention test of the memory block  14 , the supply of the power supply voltage VDD 1  from the power supply circuit  11  to the memory block  14  is cut off, and along with this, the electric charge accumulated in the stability capacitance  17  is discharged. Therefore, when the BIST circuit  15  performs the power-off retention test of the memory block  14 , the time (predetermined time T) taken for cutting off the supply of the power supply voltage VDD 1  from the power supply circuit  11  to the memory block  14  does not need to include waiting time for the completion of discharge of the electric charge accumulated in the stability capacitance  17 . In the first embodiment described above, the test time of the semiconductor device  10  can be greatly reduced, which contributes to cost reduction. 
       FIG. 3  shows a second embodiment of the present invention. The second embodiment ( FIG. 3 ) will be described below, but the same reference symbols as used in the first embodiment will be used to designate the same elements as described in the first embodiment ( FIG. 1 ), and a detailed description thereof will be omitted. A semiconductor device  20  of the second embodiment is the same as the semiconductor device  10  of the first embodiment except that it includes a step-down circuit  22  and includes a logic block  23  and a BIST circuit  25  instead of the logic block  13  and the BIST circuit  15 . 
     The step-down circuit  22  steps down the power supply voltage VDD 1  (voltage of the power supply line PL 1 ) to generate a power supply voltage VDD 2  and supplies the power supply voltage VDD 2  to a power supply line PL 2 . The logic block  23  and the BIST circuit  25  are the same as the logic block  13  and the BIST circuit  15  except that they receive the power supply voltage VDD 2  supplied to the power supply line PL 2  instead of the power supply voltage VDD 1  supplied to the power supply line PL 1  (except that operation voltages are different). 
     In the above second embodiment, the operation voltage of the logic block  23  is lower than the operation voltage of the memory block  14 , and an internal power supply system of the semiconductor device  20  is separated into two systems: a power supply system for the memory block  14  (power supply system with the power supply voltage VDD 1  generated by the power supply circuit  11 ) and a power supply system for the logic block  23  (power supply system with the power supply voltage VDD 2  generated by the step-down circuit  22 ), and also in such a case, the same effect as in the above first embodiment can be obtained. 
       FIG. 4  shows a third embodiment of the present invention. The third embodiment ( FIG. 4 ) will be described below, but the same reference symbols as used in the first and second embodiments will be used to designate the same elements as described in the first and second embodiments ( FIG. 1  and  FIG. 3 ), and a detailed description thereof will be omitted. A semiconductor device  30  of the third embodiment is the same as the semiconductor device  20  of the second embodiment except that it includes a power supply circuit  31  and a boost circuit  32  instead of the power supply circuit  11  and the step-down circuit  22 . 
     The power supply circuit  31  generates the power supply voltage VDD 2  using the external input voltage VDD (voltage supplied from outside via the power supply pin PE) and supplies the power supply voltage VDD 2  to the power supply line PL 2 . The boost circuit  32  boosts the power supply voltage VDD 2  (voltage of the power supply line PL 2 ) to generate the power supply voltage VDD 1  and supplies the power supply voltage VDD 1  to the power supply line PL 1 . 
     In the above third embodiment, the operation voltage of the logic block  23  is lower than the operation voltage of the memory block  14 , and an internal power supply system of the semiconductor device  30  is separated into two systems: a power supply system for the memory block  14  (power supply system of the power supply voltage VDD 1  generated by the boost circuit  32 ) and a power supply system for the logic block  23  (power supply system of the power supply voltage VDD 2  generated by the power supply circuit  31 ), and also in such a case, the same effect as in the above first embodiment can be obtained. 
     Incidentally, in the second embodiment, the example in which the operation voltage of the logic block  23  is lower than the operation voltage of the memory block  14  and the step-down circuit  22  which supplies the voltage (power supply voltage VDD 2 ) obtained by stepping down the voltage (power supply voltage VDD 1 ) of the power supply line PL 1  to the power supply line PL 2  is provided is described, but the present invention is not limited to this embodiment. Also when, for example, the operation voltage of the logic block  23  is higher than the operation voltage of the memory block  14  and instead of the step-down circuit  22 , a boost circuit which supplies a voltage obtained by boosting the voltage of the power supply line PL 1  to the power supply line PL 2  is provided, the same effect can be obtained. 
     Further, in the third embodiment, the example in which the operation voltage of the logic block  23  is lower than the operation voltage of the memory block  14  and the boost circuit  32  which supplies the voltage (power supply voltage VDD 1 ) obtained by boosting the voltage (power supply voltage VDD 2 ) of the power supply line PL 2  to the power supply line PL 1  is provided is described, but the present invention is not limited to this embodiment. Also when, for example, the operation voltage of the logic block  23  is higher than the operation voltage of the memory block  14  and instead of the boost circuit  32 , a step-down circuit which supplies a voltage obtained by stepping down the voltage of the power supply line PL 2  to the power supply line PL 1  is provided, the same effect can be obtained. 
     The invention is not limited to the above embodiments and various modifications may be made without departing from the spirit and scope of the invention. Any improvement may be made in part of all of the components.