Abstract:
A test mode controller is capable of reducing a chip area and unnecessary current consumption by integrally constructing latch units of the two test circuits. The test mode controller includes a test control block for determining a test mode between a programmable test and a wafer burn-in test to generate a reset signal and a control signal generating block for receiving a plurality of input signals activated in a wafer burn-in test to generate a plurality of test control signals in response to the reset signal and a programmable test signal activated in a programmable stress test.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a test mode controller; and, more particularly, to a test mode controller capable of reducing a chip area and current consumption by integrally constructing circuitry for performing a wafer burn-in test and a programmable stress test for testing the reliability. 
   BACKGROUND 
   In general, tests are mainly classified into two types, i.e., product tests and prove (or function) tests. The product test screens for product failures and sorts out articles of good quality from defects that can occur during wafer-processing, an assembly process, etc. 
   The prove test confirms whether or not the function or performance of a manufactured DRAM meets design specification. The product test is frequently performed during a shipping process, and thus there is required high throughput in the product test. The purpose of the prove test is to shorten a development period and raise the completion degree of the product by thoroughly carrying out the prove test in a research and development period. 
   If finding out the defects occurring during manufacturing processes by means of the product test, or finding out that the function of the actual product does not meet with the design specification, a predetermined analysis such as a failure analysis is performed for accurately diagnosing reasons for failure. In particular, it is important to diagnose where the defects occur in the DRAM beyond question. 
   The DRAM test measures three kinds of characteristics, i.e., DC, AC and function, by using a measurement system such as a memory test. As one part of the function test, a burn-in test is performed after a semiconductor chip is packaged. The burn-in test is performed such that excessive stress is exerted upon the whole DRAM. That is, a voltage and an ambient temperature higher than for conditions of actual use are imposed upon the DRAM in order to find out initial defects in its early stages. 
   The cells sorted out as defects through the test may be repaired for performing normal operations. In other words, the defective cells are replaced with redundancy cells. Furthermore, a predetermined operational condition, which is arbitrarily set using experimental data, is applied to the passed cells sorted out through the test during DRAM operation. 
   However, if there is a significant number of detects corresponding to several bits or higher, it is impossible to repair the wafer chip. Thus, this chip cannot be used. As a result, the package cost of the chip and the time for the burn-in test after packaging have been unnecessarily consumed. 
   In addition, this problem may becomes more serious in a highly integrated device so that the burn-in test becomes more and more important in order to accurately detect the defective cells vulnerable to the wafer burn-in test before the package process. In the wafer burn-in test, it is important to appropriately exert the stress on a portion where the defect may occur in adjacent cells. 
     FIG. 1  is a block diagram of a conventional circuit for a wafer burn-in test. 
   The circuit for the wafer burn-in test includes a decoder  10 , a wafer burn-in reset (WBI) unit  20 , a trigger generation unit  30 , and a plurality of latch units  40  to  46 . 
   The decoder  10  decodes input signals WA&lt; 9 &gt;, WA&lt; 10 &gt; and WA&lt; 11 &gt; to output test mode setting signals TDCOFF, TAWL, TEWL, TOWL, T 2 RBE, T 2 RBO and TSAE. The WBI reset unit  20  outputs a wafer burn-in reset signal RESETB in response to the output of the decoder  10  or a power-up signal PWU_B of an initial operation. The trigger generation unit  30  outputs a trigger signal TRIGP in response to an input signal WA&lt; 8 &gt;. 
   In addition, the plurality of latch units  40  to  46  latch the test mode setting signals TDCOFF, TAWL, TEWL, TOWL, T 2 RBE, T 2 RBO and TSAE in response to the wafer burn-in reset signal RESETB and the trigger signal TRIGP, to thereby output test mode control signals TDCOFFW, TAWLW, TEWLW, TOWLW, T 2 RBEW, T 2 RBOW and TSAEW. 
     FIG. 2  is a circuit diagram of the latch unit  40  to  46  of  FIG. 1 . Herein, the structures of all the latch units  40  to  46  are identical to one another so that description will be only focused on one latch unit  40 , for example. 
   The latch unit  40  includes NAND gates ND 1  to ND 3  and inverters INV 1  and INV 2 . The NAND gate ND 1  performs a NAND operation on input signals IN 1  and IN 2 . Herein, the input signals IN 1  and IN 2  denote the test mode setting signal TDCOFF and the trigger signal TRIGP, respectively. 
   The NAND gates ND 2  and ND 3  form a latch circuit. That is, the output of the NAND gate ND 2  is input through one terminal of the other NAND gate ND 3 , and vice versa. The NAND gate ND 2  performs a NAND operation on the output of the NAND gate ND 1  and the output of the NAND gate ND 3 . The NAND gate ND 3  performs a NAND operation on the output of the NAND gate ND 2  and wafer burn-in reset signal RESETB. The inverters IV 1  and IV 2  delay the output of the NAND gate ND 2  to output the output signal OUT. Herein, the output signal corresponds to the test control signal TDCOFFW. 
   In the latch unit of  FIG. 2 , when the input signals are activated to ‘high’, the output of the NAND gate ND 1  is latched at the NAND gates ND 2  and ND 3 . Accordingly, the latch unit  40  maintains the output signal OUT to be ‘high’ until the wafer burn-in reset signal RESETB is input thereto. 
     FIG. 3  is a block diagram of a conventional circuit for a programmable stress test. 
   The conventional circuit for the programmable stress test includes a plurality of latch units  50  to  55 , and a reset unit  56 . The plurality of latch units  50  to  55  latch a programmable test signal TEST generated according to the test mode code which occurs when the programmable test mode is selected, mode select signals TRG 1  to TRG 6  setting respective different modes, and a reset signal TWLRSTB, to thereby output the test control signals TAWLT, TEWLT, TOWLT, T 2 RBET, T 2 RBOT, and TSAET. The reset signal TWLRSTB is a signal generated according to the test mode code which is generated when the programmable test mode is selected. 
   The reset unit  56  outputs the reset signal TWLRSTB in response to the programmable test signal TSET, a mode select signal TRG 7 , and a reset control signal TRSTPB. 
   The detailed structure of each latch unit  50  to  55  is identical to that of  FIG. 2 . That is, when the programmable test signal TSET and the mode select signal TRG 1  to TRG 6  are activated to ‘high’, the latch unit maintains the output signal OUT to be ‘high’ until the wafer burn-in reset signal RESETB is input thereto. When the reset control signal TRSTPB is activated, the output signal OUT becomes ‘low’. 
     FIG. 4  is a circuit diagram of a conventional signal output unit  60 . 
   The conventional signal output unit  60  includes a plurality of NOR gates NOR 1  to NOR 6 , NAND gates ND 4  and ND 5 , and a plurality of inverters IV 3  to IV 15 . The signal output unit  60  performs a logic operation on the test control signals TAWLT, TEWLT, TOWLT, T 2 RBET, T 2 RBOT, and TSAET and the test control signals TAWLW, TEWLW, TOWLW, T 2 RBEW, T 2 RBOW, and TSAEW, so as to output predetermined output signals TEWL, TOWL, T 2 RBE, T 2 RBO, and TSAE. 
   In the conventional test mode controller, there are separately employed the wafer burn-in test circuit for controlling the wafer burn-in test mode operation, the programmable stress test circuit for controlling the programmable test mode operation, and the signal output unit  60  for combining the outputs of the wafer burn-in test circuit and the programmable stress test circuit. Therefore, an unnecessary circuit is used in the conventional test mode controller. The conventional test mode controller requires a large chip area, high current consumption, and limited operational speed. 
   SUMMARY OF THE INVENTION 
   It is, therefore, an object of the present invention to provide a test mode controller in which output signals of wafer burn-in test and programmable stress test circuits are output as one output signal through a circuit having a relatively simple structure, capable of reducing a chip area and unnecessary current consumption by integrally constructing latch units of the two test circuits. 
   In accordance with an aspect of the present invention, there is provided test mode controller including: a decoder for decoding a plurality of input signals activated in a wafer burn-in test to output a plurality of test mode setting signals; a plurality of latch units for latching the plurality of test mode setting signals in response to a plurality of mode select signals for selecting a test mode, a programmable test signal activated in a programmable stress test and a trigger signal, so as to output to a plurality of test control signals; and a signal output unit for performing logic operation on the plurality of test control signals to output predetermined output signals performing a test operation. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS  
     The above and other objects and features of the present invention will become better understood with respect to the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a block diagram of a conventional circuit for a wafer burn-in test; 
       FIG. 2  is a circuit diagram of the latch unit of  FIG. 1 ; 
       FIG. 3  is a block diagram of a conventional circuit for a programmable stress test; 
       FIG. 4  is a circuit diagram of a conventional signal output unit; 
       FIG. 5  is a block diagram of a test mode controller in accordance with the present invention; 
       FIG. 6  is a circuit diagram of a latch unit of  FIG. 5 ; and 
       FIG. 7  is a circuit diagram of a signal output unit in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION  
   A test mode controller in accordance with exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     FIG. 5  is a block diagram of a test mode controller in accordance with the present invention. 
   Referring to  FIG. 5 , the test mode controller of the present invention includes a decoder  100 , a wafer burn-in (WBI) reset unit  200 , a trigger generation unit  300 , a reset unit  400  and a plurality of latch units  500  to  560 . 
   The decoder  100  decodes input signals WA&lt; 9 &gt;, WA&lt; 10 &gt; and WA&lt;ll&gt; activated in a wafer burn-in test so as to output test mode setting signals TDCOFF, TAWL, TEWL, TOWL, T 2 RBE, T 2 RBO and TSAE. 
   Herein, the test mode setting signal TAWL is a signal for testing all the word lines. The test mode setting signal TEWL is a signal for testing even-number of word lines (0, 2, 4, 6, . . . ), whereas the test mode setting signal TOWL is a signal for testing odd-number of word lines (0, 1, 3, 5, . . . ). 
   The test mode setting signals T 2 RBE and T 2 RBO are signals for enabling word lines in pairs, e.g., even-number of word lines in pairs (2, 3, 6, 7, . . . ) or even-number of word lines in pairs (0, 1, 4, 5, . . . ), respectively, by means of a 2RB pattern stress application method. 
   The WBI reset unit  200  outputs a wafer burn-in reset signal RESETB in response to the output of the decoder  100  or a power-up signal PWU_B of initial operation. The trigger generation unit  300  outputs a trigger signal TRIGP using a wafer burn-in code, i.e., an input signal WA&lt; 8 &gt;, as a wafer burn-in strobe signal. 
   The reset unit  400  outputs a reset signal TWLRSTB in response to a programmable test signal TSET, a mode select signal TRG 8  for setting respective different modes, and a reset control signal TRSTPB, in which the programmable test signal TSET is generated according to a test mode code which is generated when the programmable test mode is selected. The reset signal TWLRSTB is a signal generated according to the test mode code which is generated when the programmable test mode is selected, and it is generated in response to the programmable test signal TSET, the mode select signal TRG 8 , and the reset control signal TRSTPB. 
   The plurality of latch units  500  to  560  latch the mode select signals TRG 1  to TRG 7 , the test mode setting signals TDCOFF, TAWL, TEWL, TOWL, T 2 RBE, T 2 RBO, and TSAE, the programmable test signal TSET, the wafer burn-in reset signal RESETB, the trigger signal TRIGP, and the reset signal TWLRSTB, to thereby output test control signals TDCOFFI, TAWLI, TEWLI, TOWLI, T 2 RBEI, T 2 RBOI, and TSAEI, respectively. 
   The latch unit  500  latches the mode select signal TRG 1 , the test mode setting signal TDCOFF, the programmable test signal TSET, the wafer burn-in reset signal RESETB, the trigger signal TRIGP, and the reset signal TWLRSTB so as to output the test control signal TDCOFFI. The latch unit  510  latches the mode select signal TRG 2 , the test mode setting signal TAWL, the programmable test signal TSET, the wafer burn-in reset signal RESETB, the trigger signal TRIGP, and the reset signal TWLRSTB so as to output the test control signal TAWLI. 
   The latch unit  520  latches the mode select signal TRG 3 , the test mode setting signal TEWL, the programmable test signal TSET, the wafer burn-in reset signal RESETB, the trigger signal TRIGP, and the reset signal TWLRSTB so as to output the test control signal TEWLI. Likewise, the latch unit  530  latches the mode select signal TRG 4 , the test mode setting signal TOWL, the programmable test signal TSET, the wafer burn-in reset signal RESETB, the trigger signal TRIGP, and the reset signal TWLRSTB so as to output the test control signal TOWLI. 
   The latch unit  540  latches the mode select signal TRG 5 , the test mode setting signal T 2 RBE, the programmable test signal TSET, the wafer burn-in reset signal RESETB, the trigger signal TRIGP, and the reset signal TWLRSTB so as to output the test control signal T 2 RBEI. The latch unit  550  latches the mode select signal TRG 6 , the test mode setting signal T 2 RBO, the programmable test signal TSET, the wafer burn-in reset signal RESETB, the trigger signal TRIGP, and the reset signal TWLRSTB so as to output the test control signal T 2 RBOI. 
   Likewise, the latch unit  560  latches the mode select signal TRG 7 , the test mode setting signal TSAE, the programmable test signal TSET, the wafer burn-in reset signal RESETB, the trigger signal TRIGP, and the reset signal TWLRSTB so as to output the test control signal TSAEI. 
     FIG. 6  is a circuit diagram of a latch unit of  FIG. 5 . Herein, the detail structures of the latch units  500  to  560  are identical to one another so the description will be focused on the structure of the latch unit  500  for example. 
   The latch unit  500  includes NAND gates ND 6  to ND 10 , a NOR gate NOR 7 , and inverters INV 6  to INV 8 . The NAND gate ND 6  performs a NAND operation on input signals IN 1  and IN 2 . The NAND gate ND 7  performs a NAND operation on input signals IN 3  and IN 4 . Herein, the input signals IN 1  to IN 4  means the test mode setting signal TDCOFF, the trigger signal TRIGP, the programmable test signal TSET, the mode select signal TRG 6 , respectively. The NAND gate ND 8  performs a NAND operation on the outputs of the NAND gates ND 6  and ND 7 . 
   The NAND gates ND 9  and ND 10  form a latch circuit. That is, the output of the NAND gate ND 9  is input through one terminal of the other NAND gate ND 10 , and vice versa. The NAND gate ND 9  performs a NAND operation on the output of the NAND gate ND 8  which is inverted through the inverter INV 6  and the output of the NAND gate ND 10 . The NOR gate NOR 7  performs a NOR operation on the wafer burn-in reset signal RESETB and the inversion signal TWLRST of the reset signal TWLRSTB. 
   The NAND gate ND 10  performs a NAND operation on the output of the NAND gate ND 9  and the output of the NOR gate NOR 7 . The inverters IV 8  and IV 9  delay the output of the NAND gate ND 9  to thereby output the output signal OUT. Herein, the output signal means the test control signal TDCOFFI. 
     FIG. 7  is a circuit diagram of a signal output unit  600  in accordance with the present invention. 
   The signal output unit  600  includes NAND gates ND 11  and ND 12 , and a plurality of inverters IV 19  to IV 28 . The signal output unit  600  performs a logic operation on the test control signals TAWLI, TEWLI, TOWLI, T 2 RBEI, T 2 RBOI, and TSAEI to output the output signals TEWL, TOWL, T 2 RBE, T 2 RBO, and TSAE. 
   The NAND gate ND 11  performs logic NAND operation on the test control signals TAWLI and TEWLI. The NAND gate ND 12  performs logic NAND operation on the test control signals TAWLI and TOWLI. The inverters IV 19  and IV 20  delay the output of the NAND gate ND 11  to output the output signal TEWL. The inverters IV 21  and IV 22  delay the output of the NAND gate ND 12  to output the output signal TOWL. 
   The inverters IV 23  and IV 24  delay the test control signal T 2 RBEI, to thereby output the output signal T 2 RBE. Likewise, the inverters IV 25  and IV 26  delay the test control signal T 2 RBOI so as to output the output signal T 2 RBO. The inverters IV 27  and IV 28  delay the test control signal TSAEI to output the output signal TSAE. 
   An operational mechanism of the test mode controller in accordance with the present invention will be set forth as followings. 
   In the inventive test mode controller, there are integrally formed the wafer burn-in test circuit for performing reliability test and the latch units  500  to  560  for performing the programmable stress test. 
   First, the decoder  100  decodes the input signals WA&lt; 9 &gt;, WA&lt; 10 &gt;, and WA&lt; 11 &gt; which are activated during the wafer burn-in  test so as to output the test mode setting signals TDCOFF, TAWL, TEWL, TOWL, T 2 RBE, T 2 RBO, and TSAE to the respective latch units  500  to  560 . 
   When both of the input signals IN 1  and IN 2 , i.e., the test mode setting signal TDCOFF and the trigger signal TRIGP, are activated to ‘high’, the output signal OUT of the latch unit  500  becomes ‘high’. In addition, when both of the input signals IN 3  and IN 4 , i.e., the programmable test signal TSET and the mode select signal TRGn, are activated to ‘high’, the output signal OUT of the latch unit  500  becomes ‘high’. 
   Since the other latch units  510  to  560  have the same structures as the latch unit  500 , they latch the respective input signals to output the respective signals OUT. 
   In the inventive test mode controller, although only one of the wafer burn-in test mode and the programmable test mode is enabled, the latch unit  500  outputs the output signal OUT of logic high level. Accordingly, the output signal OUT is maintained to be ‘high’ until the activated wafer burn-in reset signal RESETB or the reset signal TWLRST is input. 
   When the power up signal PWU_B is activated, the wafer burn-in reset signal RESETB is activated according to the output of the decoder  100  for the wafer burn-in test, or the programmable stress reset signal TWLRST generated according to the test mode code is activated, the latch circuit of the latch unit  500  is reset. 
   The signal output unit  600  performs logic operation on the test control signals TDCOFFI, TAWLI, TEWLI, TOWLI, T 2 RBEI, T 2 RBOI, and TSAEI, which are applied from the respective latch units  500  to  560 , to thereby generate the output signals TEWL, TOWL, T 2 RBE, T 2 RBO, and TSAE for controlling the test mode. 
   In the conventional test mode controller, two signals required for controlling the wafer burn-in test and the programmable stress test mode should be integrated as one signal via the NOR gate. However, in accordance with the present invention, the output signal, which has been already integrated at the integrally-constructed latch units  500  to  560 , is applied to the signal output unit  600  and thereafter, each signal is output after buffering. 
   As described above, in accordance with the present invention, the output signals of the wafer burn-in test circuit and the programmable stress test circuit are output as one signal via the inventive circuit having a simple structure. Furthermore, the latch units of the two circuits are integrally formed so that it is possible to reduce the chip area and the current consumption, and to enhance the test speed. 
   The present application contains subject matter related to the Korean patent applications Nos. 10-2005-91660 and 10-2006-29650, filed in the Korean Patent Office on Sep. 29, 2005 and Mar. 31, 2006 respectively, the entire contents of which being incorporated herein by reference. 
   While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.