Abstract:
A resistance change memory device includes: a memory chip having memory cells of a resistance change type; and a heater so attached to the memory chip as to apply a temperature bias to the memory chip.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based on and claims the benefit of priority from the prior Japanese Patent Application No. 2007-171939, filed on Jun. 29, 2007, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates to a resistance change memory device, in which memory cells of a resistance-change type are used, and an integrated circuit device with a resistance change memory chip. 
         [0004]    2. Description of the Related Art 
         [0005]    A resistance change memory device has been proposed to store a resistance value as data, which is reversibly rewritten by applying voltage, current or heat, and it is noticed for succeeding to the conventional flash memory. This resistance change memory is suitable for miniaturizing the cell size, and for constituting a cross-point cell array. In addition, it is easy to stack cell arrays. 
         [0006]    As a heat process adapted for resetting a data state of the resistance change memory device, it is usually used Joule&#39;s heat generated by applying a certain voltage or current to a memory cell. If it takes a long time to perform this heat process, it prevents the resistance change memory from being progressed in high speed performance and low power consumption. 
         [0007]    It has been proposed a phase change memory made of a chalcogenide layer, which is a kind of resistance change memory and has a heater attached to the chalcogenide layer (for example, refer to JP 2005-71500A). Further, there has also been proposed a magnetic memory device, in which heater layers are disposed at every memory cell for partially heating them and accelerating the data state change of memory cells (for example, refer to JP 2005-136419A). 
         [0008]    It has also been proposed such a technology that a heater is installed on an integrated circuit device for adjusting the environmental temperature (for example, refer to JP 4-206861A). 
       SUMMARY OF THE INVENTION 
       [0009]    According to an aspect of the present invention, there is provided a resistance change memory device including: 
         [0010]    a memory chip having memory cells of a resistance change type; and 
         [0011]    a heater so attached to the memory chip as to apply a temperature bias to the memory chip. 
         [0012]    According to another aspect of the present invention, there is provided an integrated circuit device including: 
         [0013]    a substrate; 
         [0014]    a memory chip mounted on the substrate, the memory chip having memory cells of a resistance change type; 
         [0015]    a circuit chip mounted on the substrate, the maximum power consumption of which is larger than that of the memory chip; and 
         [0016]    a thermal conductive plate disposed to extend over the circuit chip and the memory chip. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  shows an equivalent circuit of a memory cell array in accordance with an embodiment of the present invention. 
           [0018]      FIG. 2  shows a stacked structure of the memory cell. 
           [0019]      FIG. 3  is a diagram for explaining memory operation modes of a variable resistance element. 
           [0020]      FIG. 4  shows a potential distribution for explaining the memory operation modes. 
           [0021]      FIG. 5  is a diagram for explaining memory operation modes of another variable resistance element. 
           [0022]      FIG. 6  shows a heater attached state of the memory chip. 
           [0023]      FIG. 7  shows another heater attached state of the memory chip in a package. 
           [0024]      FIG. 8  shows another example, in which a circuit chip is used as a heater of the memory chip. 
           [0025]      FIG. 9  shows a layout, in which a heater is disposed for heating only the memory cell area in the memory chip. 
           [0026]      FIG. 10  shows another example modified from that shown in  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0027]    Illustrative embodiments of this invention will be explained with reference to the accompanying drawings below. 
         [0028]      FIG. 1  shows an equivalent circuit of memory cell array MA in accordance with an embodiment. As shown in  FIG. 1 , word lines WL and bit lines BL are disposed to cross each other, and resistance change memory cells MC. Memory cell MC is formed of access element, e.g., diode, Di and variable resistance element VR, which are connected in series and disposed at a cross point between word line WL and bit line BL. 
         [0029]    Variable resistance element VR has a stacked structure of electrode/transition metal oxide/electrode. In accordance with voltage, current or heat application condition, the resistance value of the metal oxide layer is changed, so that the element VR stores one of different resistance states as data in a non-volatile manner. This kind of variable resistance element VR is formed to be operable as a bipolar type of or a unipolar type of element. The cell array arrangement shown in  FIG. 1  is a case of the unipolar type. 
         [0030]    Assuming that the memory cell MC is kept in a high resistance value state as a stable state (i.e., reset state), it stores, for example, binary data defined by the high resistance state and a low resistance state (i.e., set state). 
         [0031]    The stack structure of the memory cell MC is shown in  FIG. 2 . That is, variable resistance element VR and access element Di are stacked at the cross point of metal wirings  21  and  22 , which serves as bit line BL and word line WL, respectively, thereby constituting memory cell MC. 
         [0032]      FIG. 3  is a diagram for explaining a data storage mode of an example of the variable resistance element VR. This element VR has a stacked structure of first metal oxide layer  31  and second metal oxide layer  32 , and electrodes  33  and  34  formed on the stacked structure. 
         [0033]    Explaining in detail, the first metal oxide layer  31  is Mn-oxide containing Mg; and the second metal oxide layer  32  is Ti-oxide including a cavity site. “L” shown in the compound expression designates the cavity site. 
         [0034]    The left side in  FIG. 3  shows a high resistive and stable state that the second metal oxide layer  32  has the cavity site. This state is defined as a reset state. Applying voltage between electrodes  33  and  34  with such a polarity that electrode  33  becomes positive, Mg ion in the first metal oxide layer  31  moves into the second metal oxide layer  32  to be trapped in the cavity site in accordance with the electric field formed therein, so that a low resistance state (i.e., set state) will be obtained. 
         [0035]    The reset process is defined as a heat process. Applying voltage to the device, a large current flows because it is in the low resistance state, and Joule&#39;s heat is generated. As a result of this heat energy, Mg ion trapped in the cavity site in the second metal oxide layer  32  will be released to the first metal oxide layer  31 , so that the high resistance state is restored. 
         [0036]      FIG. 4  shows electrochemical potential distributions of the variable resistance element VR, as corresponding to the reset and set states shown in  FIG. 3 . Explaining briefly, the reset state is a stable state, in which the electrochemical potential is low, and defined as a high resistance state. Applying an electric field that is able to get over the barrier potential P 1  shown in  FIG. 4 , the low resistance state may be set based on the metal ion (Mg ion) movement (referred to as a set operation). 
         [0037]    On the other hand, applying a heat energy that is able to get over the barrier potential P 2  required to hold the low resistance state, the state will be restored to be in the high resistance state defined as a thermally stabilized state (referred to as a reset operation). 
         [0038]    Note here that it is able to use the state transition between a crystalline state and an amorphous state of the cell material as the variable resistance element VR (i.e., phase change in the narrow sense).  FIG. 5  shows a variable resistance element VR using the above-described phase change. 
         [0039]    In this case, the recording layer  51  sandwiched between electrodes  52  and  53  is formed of a chalcogenide layer. Heating and then gradually cooling it to crystallize itself, the recording layer  51  is set to be in a low resistance state (i.e., conductor). This is referred to as a rest operation. By contrast, cooling fast after heating the device in the set state, the chalcogenide layer  51  is reset to be in an amorphous and high resistance state (i.e., insulator). 
         [0040]    In the above-described resistance change memory device in accordance with this embodiment, the memory chip has a heater prepared for applying a temperature bias for accelerating the heat process of the state change of the memory device (i.e., variable resistance element). The detail will be explained below. 
         [0041]      FIG. 6  is an example, in which electrodes  62  are arranged on one surface of a resistance change memory chip  61  and heater  63  is attached on the other surface. When turning on the power supply of the memory chip  61 , the heater  63  is simultaneously turned on the electricity. 
         [0042]    With this configuration, a certain temperature bias may be applied to the memory cells in the memory chip  61 , so that the heat process is accelerated. As a result, it becomes possible to access the resistance change memory at a high speed, and the power consumption will be reduced. 
         [0043]    In another example shown in  FIG. 7 , heater  72  is put on resistance change memory chip  71 , and these are installed in package  73 . In this case, a certain kind of circuit chip, e.g., CPU chip, may be used as heater  72 . As a result, heat of the circuit chip is effectively used for temperature bias of the memory chip  71 , so that it becomes possible to access the resistance change memory at a high speed, and the power consumption will be reduced. 
         [0044]      FIG. 8  shows an integrated circuit device in accordance with still another embodiment, which has resistance change memory chip  81  and a circuit chip  82  mounted on a substrate  80 . The maximum power consumption of the circuit chip  82  is larger than that of the memory chip  81 . Therefore, the circuit chip  82  serves as a thermal source for heating the memory chip  81 . 
         [0045]    Explaining in detail more, thermal conductive plate  83  is disposed to extend over the circuit chip  82  and memory chip  81 . In a more desirable example, the thermal conductive plate  83  has first and second conductive chips  83   a  and  83   b  disposed on the circuit chip  82  and memory chip  81 , respectively, and thermal resistive chip  84  disposed between these thermal conductive chips  83   a  and  83   b  for adjusting the thermal conductivity between the circuit chip  82  and memory chip  81 . 
         [0046]    The thermal conductive plate  83  also serves as a radiator for the circuit chip  82  with large power consumption. Therefore, the circuit chip  82  serving as a heat source, the bias temperature of the memory chip  81  may be made to be optimal. Further, it becomes possible to access the resistance change memory at a high speed, and the power consumption will be reduced. 
         [0047]      FIG. 9  shows still another example, in which heater  94  is located for heating only memory cell array areas  92   a  and  92   b  in the resistance change memory chip  91 . Peripheral circuit area  93  in the memory chip  91  is not heated. 
         [0048]    In general, a transistor circuit in an integrated circuit becomes slow in operation speed in accordance with temperature rising. Arranging the heater  94  to be limited to the cell array area, the memory cell operation will be made to be fast without reducing the operation speed of the peripheral circuit  93 . 
         [0049]      FIG. 10  shows another example, which is the same as that shown in  FIG. 9  except that temperature detecting circuit  95  is formed in the memory chip  91 . The measurement result of the temperature detecting circuit  95  is supplied to a controller  96  in the peripheral circuit  93 , and serves for controlling the operation speed of the memory. The data state transition speed of the memory device depends on temperature. Therefore, controlling the operation speed in accordance with the memory chip temperature, it becomes possible to achieve a suitable memory operation speed. 
         [0050]    This invention is not limited to the above-described embodiments. It will be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit, scope, and teaching of the invention.