Abstract:
A gating device cell for a cross array of bipolar resistive memory cells comprises an n-p diode and a p-n diode, wherein the n-p diode and the p-n diode have opposite polarities and are connected in parallel, such that the gating device cell exhibits a bidirectional rectification feature. The gating device cell exhibits the bidirectional rectification feature, that is, it can provide a relatively high current density at any voltage polarity in its ON state, and also a relatively great rectification ratio (R v/2 /R V ) under a read voltage. Therefore, it is possible to suppress read crosstalk in the cross array of bipolar resistive memory cells to avoid misreading, thereby solving the problem that a conventional rectifier diode is only applicable to a cross array of unipolar resistive memory cells.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application is a U.S. national phase application of PCT Application No. PCT/CN2013/084063 filed on Mar. 15, 2013, entitled “GATE DEVICE UNIT FOR CROSS ARRAY INTEGRATION MODE OF BIPOLAR RESISTIVE RANDOM ACCESS MEMORY,” which claims priority to Chinese Application No. 201310084292.7 filed on Mar. 15, 2013. Both the PCT Application and the Chinese Application are incorporated herein by reference in their entireties. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to the microelectronic technology, and in particular, to a gating device cell for a cross array of bipolar resistive memory cells. 
       BACKGROUND 
       [0003]    As an emerging non-volatile memory technology, Resistive Random Access Memories (RRAMs) have great advantages in many aspects, such as, device structure, cell area, storage density, power consumption, programming/erasing speed, 3D integration and multi-value storage, and are becoming one of the most powerful competitors in replacing “flash” memories which are currently mainstream products in the non-volatile memory market. A sandwich structure of Metal/Insulator/Metal (MIM) is a basic structure for the resistive memory, and such a vertical MIM structure is beneficial for cross-array integration to achieve super high density storage. In a cross-array structure, cross points between upper and lower lines which are perpendicular to each other contain memory cells, each of which can achieve gating and reading/writing. 
         [0004]    However, the existing resistive memory cell has a symmetric read current-voltage curve under positive and negative voltage polarities. As shown in  FIG. 1 , when the resistor memory cell is in a low resistance state and a range of—V read →V read  is Direct Current (DC) scanned, this device presents a symmetric current-voltage curve under positive and negative voltage polarities. When a cross-array memory architecture is used, a memory cell in the low resistance state will provide an additional leakage path due to the symmetric read electrical characteristic of the memory cell. Such a leakage path will impact information read from a gated memory cell and cause a serious read crosstalk problem in the cross array. As shown in  FIG. 2 , among four neighboring memory cells, a cell at coordinates ( 1 ,  1 ) is in a high resistance state, and the other three cells ( 1 ,  2 ), ( 2 ,  2 ), and ( 2 ,  1 ) are all in a low resistance state. When a read voltage is applied to the device ( 1 ,  1 ), the current may flow along the low resistance path ( 1 ,  2 )→( 2 ,  2 )→( 2 ,  1 ) (shown by the dashed line), such that the device ( 1 ,  1 ) is misread as an ON state (or a low resistance state). 
         [0005]    In the prior art, the misreading phenomenon may be effectively addressed by connecting a rectifier diode to the resistive memory cell in series. However, because the rectifier diode generally shows an ON feature only in the forward direction but cannot provide enough current in the reverse direction, the resistive memory cell that currently can be integrated with the rectifier diode must have a unipolar resistance switching feature. That is, programming and erasing operations for the resistive memory cell must be done in the same voltage polarity. For a more popular bipolar resistive memory cell, its programming and erasing operations must be done in opposite voltage polarities, and therefore a single rectifier diode cannot meet the current requirement for its erasing in the reverse direction. As a result, the misreading phenomenon caused by the read crosstalk in a cross array of bipolar resistive memory cells cannot be effectively addressed up to now. 
       SUMMARY 
     Technical Problem To Be Solved 
       [0006]    In view of the above, an object of the present disclosure is to provide a gating device cell that is applicable to a cross array of bipolar resistive memory cells, so as to suppress the misreading phenomenon caused by the read crosstalk in the cross array of bipolar resistive memory cells. 
       Technical Solutions 
       [0007]    To achieve the above object, the present disclosure provides a gating device cell for a cross array of bipolar resistive memory cells. The gating device cell comprises an n-p diode and a p-n diode. The n-p diode and the p-n diode have opposite polarities and are connected in parallel, such that this gating device cell exhibits a bidirectional rectification feature. 
         [0008]    According to an embodiment, the n-p diode and the p-n diode are connected in parallel with a dielectric isolation layer interposed therebetween. The dielectric isolation layer may comprise one of SiO 2 , Si 2 N 3 , HfO 2 , ZrO 2 , or Al 2 O 3 . 
         [0009]    According to an embodiment, the n-p diode comprises a first lower conductive electrode, a first n-type doped semiconductor layer, a first p-type doped semiconductor layer, and a first upper conductive electrode that are stacked sequentially from bottom to top, and the p-n diode comprises a second lower conductive electrode, a second p-type doped semiconductor layer, a second n-type doped semiconductor layer, and a second upper conductive electrode that are stacked sequentially from bottom to top. 
         [0010]    According to an embodiment, the first lower conductive electrode and the second lower conductive electrode each comprise a metallic material or a conductive metallic compound. Materials for the first lower conductive electrode and the second lower conductive electrode may be the same or different. The metallic material comprises at least one selected from a group consisting of W, Al, Cu, Au, Ag, Pt, Ru, Ti, Ta, Pb, Co, Mo, Ir, and Ni, and the conductive metallic compound comprises at least one selected from a group consisting of TiN, TaN, IrO 2 , ITO, and IZO. 
         [0011]    According to an embodiment, the first lower conductive electrode and the second lower conductive electrode each are prepared by any of electron beam evaporation, chemical vapor deposition, pulsed laser deposition, atom layer deposition, or magnetron sputtering. 
         [0012]    According to an embodiment, the first lower conductive electrode and the second lower conductive electrode each have a thickness of 1 nm-500 nm. 
         [0013]    According to an embodiment, the first n-type doped semiconductor layer and the first p-type doped semiconductor layer form an n-p junction, which comprises a semiconductor material of Si, Ge, GaAs, InP, or SiGe modified by doping, and the second p-type doped semiconductor layer and the second n-type doped semiconductor layer form a p-n junction, which comprises a semiconductor material of Si, Ge, GaAs, InP, or SiGe modified by doping. The doping may be done by thermal diffusion or ion implantation, at a doping concentration of 1×10 12  cm −2 -1×10 22  cm −2 . The gating device cell may have a positive ON voltage controlled by a doping concentration or a junction depth of the n-p junction in the n-p diode and a negative ON voltage controlled by a doping concentration or a junction depth of the p-n junction in the p-n diode. 
         [0014]    According to an embodiment, the first n-type doped semiconductor layer, the first p-type doped semiconductor layer, the second p-type doped semiconductor layer, and the second n-type doped semiconductor layer each are prepared by any of chemical vapor deposition, atom layer deposition, and molecular beam epitaxy. 
         [0015]    According to an embodiment, the first n-type doped semiconductor layer, the first p-type doped semiconductor layer, the second p-type doped semiconductor layer, and the second n-type doped semiconductor layer each have a thickness of 10 nm-500 nm. 
         [0016]    According to an embodiment, the first upper conductive electrode and the second upper conductive electrode each comprise a metallic material or a conductive metallic compound. Materials for the first upper conductive electrode and the second upper conductive electrode may be the same or different. The metallic material comprises at least one selected from a group consisting of W, Al, Cu, Au, Ag, Pt, Ru, Ti, Ta, Pb, Co, Mo, Ir, and Ni, and the conductive metallic compound comprises at least one selected from a group consisting of TiN, TaN, IrO 2 , ITO, and IZO. 
         [0017]    According to an embodiment, the first upper conductive electrode and the second upper conductive electrode each are prepared by any of electron beam evaporation, chemical vapor deposition, pulsed laser deposition, atom layer deposition, or magnetron sputtering. 
         [0018]    According to an embodiment, the first upper conductive electrode and the second upper conductive electrode each have a thickness of 1 nm-500 nm. 
       Advantageous Effects 
       [0019]    As can be seen from the above technical solutions, the present disclosure has following advantageous effects. 
         [0020]    The gating device cell for a cross array of bipolar resistive memory cells disclosed herein is formed by connecting a diode of the n-p type semiconductor material which can turn ON in the positive direction and a diode of the p-n type semiconductor material which can turn ON in the negative direction in parallel. The n-p diode turns ON under a positive voltage and turns OFF under a negative voltage; and the p-n diode turns on under a negative voltage and turns OFF under a positive voltage. When the n-p diode and the p-n diode are connected in parallel, a relatively great ON current and a relatively great non-linear resistance coefficient can be provided in both of the positive and negative voltage directions, thereby effectively suppressing the misreading phenomenon caused by read crosstalk in the cross array of bipolar resistive memory cells. 
         [0021]    Further, the gating device cell for a cross array of bipolar resistive memory cells disclosed herein is formed by connecting two rectifier diodes of opposite polarities in parallel. Its structure is shown in  FIG. 3 . It may serve as a gating diode for the bipolar resistive memory, and can provide a relatively great ON current and a relatively great non-linear resistance coefficient in both of the positive and negative voltage directions, while maintaining a relatively good bidirectional rectification feature. That is, a relatively high current density can be provided in any voltage polarity when in the ON state. Further, it is possible to provide a relatively great rectification ratio (R v/2 /R V ) under a read voltage. Therefore, it is possible to suppress the read-crosstalk phenomenon in the cross array of bipolar resistive memory cells to avoid misreading, thereby solving the problem that a conventional rectifier diode is only applicable to a cross array of unipolar resistive memory cells. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    To further illustrate the concept of the present disclosure, a detailed description of the present disclosure will be given with reference to the drawings and embodiments, in which: 
           [0023]      FIG. 1  is a current-voltage curve for a read operation of a resistive memory cell in a low resistance state in the prior art; 
           [0024]      FIG. 2  is a diagram showing a read crosstalk problem in a cross array of resistive memory cells in the prior art; 
           [0025]      FIG. 3  is a structural diagram showing a gating device cell for a cross array of resistive memory cells according to an embodiment of the present disclosure, wherein  11  denotes an n-p diode,  12  denotes a p-n diode,  101  denotes a lower conductive electrode,  102  denotes an n-type semiconductor layer,  103  denotes a p-type semiconductor layer,  104  denotes an upper conductive electrode,  105  denotes a lower conductive electrode,  106  denotes a p-type semiconductor layer,  107  denotes an n-type semiconductor layer,  108  denotes an upper conductive electrode, and  109  denotes an isolation dielectric layer; 
           [0026]      FIG. 4  is a current-voltage characteristic curve of an n-p junction diode included in a gating device cell in a DC scanning mode according to an embodiment of the present disclosure; 
           [0027]      FIG. 5  is a current-voltage characteristic curve of a p-n junction diode included in a gating device cell in a DC scanning mode according to an embodiment of the present disclosure; 
           [0028]      FIG. 6  is a current-voltage characteristic curve of an n-p junction diode and a p-n junction diode, which are connected in parallel, in a gating device cell in a DC scanning mode according to an embodiment of the present disclosure; 
           [0029]      FIG. 7  is a current-voltage characteristic curve of a bipolar resistive memory cell in a DC scanning mode according to an embodiment of the present disclosure; 
           [0030]      FIG. 8  is a diagram showing an arrangement for applying a read/write voltage of V/ 2  to a cross array of cells, each of which is formed by connecting a bipolar resistive memory cell and a gating device in series, according to an embodiment of the present disclosure; and 
           [0031]      FIG. 9  is a read current-voltage characteristic curve of a bipolar resistive memory cell connected in series with a gating device in a DC scanning mode according to an embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    To make objects, solutions, and advantages of the present disclosure apparent, detailed description will be given in conjunction with specific embodiments with reference to the drawings. 
         [0033]      FIG. 3  is a structural diagram showing a gating device cell for a cross array of bipolar resistive memory cells according to an embodiment of the present disclosure. As shown in  FIG. 3 , this gating device cell comprises an n-p diode  11  and a p-n diode  12 . The n-p diode  11  and the p-n diode  12  have opposite polarities and are connected in parallel, such that this gating device cell exhibits a bidirectional rectification feature. 
         [0034]    The n-p diode  11  and the p-n diode  12  are connected in parallel with a dielectric isolation layer  109  interposed therebetween. The dielectric isolation layer  109  may comprise any one of SiO 2 , Si 2 N 3 , HfO 2 , ZrO 2 , or Al 2 O 3 . 
         [0035]    The n-p diode  11  comprises a first lower conductive electrode  101 , a first n-type doped semiconductor layer  102 , a first p-type doped semiconductor layer  103 , and a first upper conductive electrode  104  that are stacked sequentially from bottom to top, and the p-n diode  12  comprises a second lower conductive electrode  105 , a second p-type doped semiconductor layer  106 , a second n-type doped semiconductor layer  107 , and a second upper conductive electrode  108  that are stacked sequentially from bottom to top. 
         [0036]    The first lower conductive electrode  101  and the second lower conductive electrode  105  each may comprise a metallic material or a conductive metallic compound. The first lower conductive electrode  101  and the second lower conductive electrode  105  may comprise the same material or different materials. The metallic material may comprise at least one selected from a group consisting of W, Al, Cu, Au, Ag, Pt, Ru, Ti, Ta, Pb, Co, Mo, Ir, and Ni, and the conductive metallic compound may comprise at least one selected from a group consisting of TiN, TaN, IrO 2 , ITO, and IZO. 
         [0037]    The first lower conductive electrode  101  and the second lower conductive electrode  105  each may be prepared by any one of electron beam evaporation, chemical vapor deposition, pulsed laser deposition, atom layer deposition, or magnetron sputtering. The first lower conductive electrode  101  and the second lower conductive electrode  105  each may have a thickness of 1 nm-500 nm. 
         [0038]    The first n-type doped semiconductor layer  102  and the first p-type doped semiconductor layer  103  form an n-p junction, which may comprise a semiconductor material, such as Si, Ge, GaAs, InP, or SiGe, modified by doping. The second p-type doped semiconductor layer  106  and the second n-type doped semiconductor layer  107  form a p-n junction, which may comprise a semiconductor material, such as Si, Ge, GaAs, InP, or SiGe, modified by doping. The doping can be done by thermal diffusion or ion implantation, at a doping concentration of 1×10 12  cm −2 -1×10 22  cm −2 . The gating device cell may have a positive ON voltage controlled by the doping concentration or a junction depth of the n-p junction in the n-p diode and a negative ON voltage controlled by the doping concentration or a junction depth of the p-n junction of the p-n diode. 
         [0039]    The first n-type doped semiconductor layer  102 , the first p-type doped semiconductor layer  103 , the second p-type doped semiconductor layer  106 , and the second n-type doped semiconductor layer  107  each may be prepared by any one of chemical vapor deposition, atom layer deposition, or molecular beam epitaxy. The first n-type doped semiconductor layer  102 , the first p-type doped semiconductor layer  103 , the second p-type doped semiconductor layer  106 , and the second n-type doped semiconductor layer  107  each may have a thickness of 10 nm-500 nm. 
         [0040]    The first upper conductive electrode  104  and the second upper conductive electrode  108  each may comprise a metallic material or a conductive metallic compound. The first upper conductive electrode  104  and the second upper conductive electrode  108  may comprise the same material or different materials. The metallic material may comprise at least one selected from a group consisting of W, Al, Cu, Au, Ag, Pt, Ru, Ti, Ta, Pb, Co, Mo, Ir, and Ni, and the conductive metallic compound may comprise at least one selected from a group consisting of TiN, TaN, IrO 2 , ITO, and IZO. 
         [0041]    The first upper conductive electrode  104  and the second upper conductive electrode  108  each may be prepared by any one of electron beam evaporation, chemical vapor deposition, pulsed laser deposition, atom layer deposition, or magnetron sputtering. The first upper conductive electrode  104  and the second upper conductive electrode  108  each may have a thickness of 1 nm-500 nm. 
         [0042]    According to the embodiment of the present disclosure, the gating device cell is formed by connecting the n-p diode and the p-n diode in parallel. This gating device cell may have an effect of suppressing the read crosstalk in the cross array of bipolar resistive memory cells. 
         [0043]      FIG. 4  is a current-voltage characteristic curve of an n-p junction diode included in a gating device cell in a DC scanning mode according to an embodiment of the present disclosure. When the positive scanning voltage exceeds V 1 , the n-p diode turns ON in the positive direction, and thus is in a low resistance state; while under the negative scanning voltage, the n-p diode is in an OFF state and thus in a high resistance state. 
         [0044]      FIG. 5  is a current-voltage characteristic curve of a p-n junction diode included in a gating device cell in a DC scanning mode according to an embodiment of the present disclosure. The characteristic of the p-n diode is opposite to that of the n-p diode. When the negative scanning voltage exceeds V 2  in absolute value, the p-n diode turns ON in the negative direction, and thus is in a low resistance state; while under the positive scanning voltage, the p-n diode is in an OFF state and thus in a high resistance state. 
         [0045]      FIG. 6  is a current-voltage characteristic curve of an n-p junction diode and a p-n junction diode, which are connected in parallel, in a gating device cell in a DC scanning mode according to an embodiment of the present disclosure. When the positive scanning voltage exceeds V 1 , the n-p diode turns ON, that is, the gating device turns ON; while when the negative scanning voltage exceeds V 2  in absolute value, the p-n diode turns ON such that the gating device turns ON. As can be seen from  FIG. 6 , the gating device formed by connecting the n-p diode and the p-n diode in parallel can provide a relatively great current in both of the positive and negative voltage directions. Therefore, the current requirements in both the positive and negative voltage polarities for programming/erasing operations of the bipolar resistive memory as shown in  FIG. 7  can be met. 
         [0046]    In addition, when the voltage across the gating device formed by connecting the n-p diode and the p-n diode in parallel is less than the ON voltage V 1  (or V 2 ), the gating device is in a relatively high resistance state. Therefore, in a cross array of cells, each of which is formed by the gating device cell of the n-p diode and the p-n diode in parallel and the bipolar resistive memory cell, an arrangement for applying a voltage of V/ 2  is used, as shown in  FIG. 8 . 
         [0047]    A ( 1 / 2 )V programming  or ( 1 / 2 )V reading  voltage is applied to a word line at which a cell to be selected is located, a (− 1 / 2 )V programming  or (− 1 / 2 )V reading  voltage is applied to a bit line at which the cell to be selected is located, and a zero bias voltage is applied to other word lines and bit lines. At this point, the voltage across the selected cell is V programming  or V reading , and the voltage across the memory cells on the same word line or the same bit line as the selected cell is (± 1 / 2 )V programming  or (± 1 / 2 )V reading , while the voltage across the remaining memory cells is zero. Therefore, with such a voltage pattern, the read crosstalk in the array is mainly originated from the memory cell(s) which is (are) in the low resistance state on the same bit line or the same word line. As can be seen from  FIG. 8 , when the selected memory cell is being read, the voltage across a memory cell on the same bit line or the same word line as the selected memory cell is (± 1 / 2 )V reading . In an embodiment of the present disclosure, the applied read voltage satisfies that V reading / 2 &lt;V 1 &lt;V reading  and |−V reading / 2 |&lt;|V 2 |&lt;|−V reading . The memory cell formed by connecting the gating device and the bipolar memory cell in series exhibits a bidirectional rectification feature during the read operation, as shown in  FIG. 9 . 
         [0048]    Under the voltage ±V reading , the memory cell exhibits a resistance of the resistive memory cell, and the gating device is in a low resistance state; while under the voltage (± 1 / 2 )V reading , the memory cell exhibits a resistance of the diode in the OFF state and therefore in a high resistance state, thereby reducing the leakage paths generated by the memory cells on the same bit line or the same word line. The present disclosure defines the rectification as R v/2 /R V . The effect of suppressing the read crosstalk in the cross array of bipolar resistive memory cells by the gating device proposed by the present disclosure is determined mainly by the rectification ratio (R v/2 /R V ). 
         [0049]    The above specific embodiments provide detailed explanations of the objects, technical solutions, and advantageous effects of the present disclosure. It is to be understood that the above descriptions are only illustrative, and the present disclosure is not limited thereto. Any modification, equivalent substitution, or improvement made within the spirit and principle of the present disclosure shall fall into the scope of the present disclosure.