Abstract:
An electrode layer for a polymer memory may be implanted to increase the number of defects in the material. As a result, that same material may be utilized for the upper and lower electrodes. In particular, defects may be introduced into a TiO x  layer within the electrode to match the work functions of the upper and lower electrodes.

Description:
BACKGROUND  
       [0001]     This invention relates generally to polymer memories.  
         [0002]     A ferroelectric polymer memory may be used to store data. The data may be stored in layers within the memory. The higher the number of layers, the higher the capacity of the memory. Each of the polymer layers includes polymer chains with dipole moments. Data may be stored by changing the polarization of the polymer between metal lines. No transistors may be needed for storage.  
         [0003]     Ferroelectric polymer memories are non-volatile memories with sufficiently fast read and write speeds. For example, microsecond initial reads may be possible with write speeds comparable to those with flash memories.  
         [0004]     Conventionally, polymer memories are formed by a layer of polymer between upper and lower parallel electrodes. Thus, successive, vertically spaced sets of horizontal metal lines may be utilized to define a polymer memory cell between upper and lower lines.  
         [0005]     Polymer memories are subject to a disturb problem. A disturb is polarization lost on a cell due to the application of a voltage less than that required to switch the cell. To overcome this problem, an electrode stack that includes different materials for the upper and lower electrodes has been suggested. For example, a TiO x  top electrode may be used with a bottom electrode made of a different material, such as titanium nitride or tantalum nitride. Although this asymmetric electrode approach has shown good results, the difference in work functions between titanium nitride and TiO x  electrodes results in differences in charge injection capability into the ferroelectric polymer.  
         [0006]     Thus, there is a need for alternate ways to overcome the disturb problem in polymer memories. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is an enlarged, cross-sectional view of one embodiment of the present invention at an early stage of manufacture;  
         [0008]      FIG. 2  is an enlarged, cross-sectional view corresponding to  FIG. 1  at a subsequent stage of manufacture in accordance with one embodiment of the present invention;  
         [0009]      FIG. 3  is a top plan view of the embodiment shown in  FIG. 2 ;  
         [0010]      FIG. 4  is an enlarged, cross-sectional view of the embodiment shown in  FIG. 3  after further processing in accordance with one embodiment of the present invention;  
         [0011]      FIG. 5  is an enlarged, cross-sectional view of the embodiment shown in  FIG. 4  after further processing in accordance with one embodiment of the present invention;  
         [0012]      FIG. 6  is an enlarged, top plan view of the embodiment shown in  FIG. 5  in accordance with one embodiment of the present invention; and  
         [0013]      FIG. 7  is a depiction of a system in accordance with one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0014]     Referring to  FIG. 1 , a polymer memory structure  10  may include a silicon substrate  12  covered by an insulator  14 . The insulator  14 , in one embodiment, may be silicon dioxide or polyimide. A lower electrode, including the layers  20 ,  18 , and  16 , may be formed over the insulator  14 . In one embodiment, the layer  16  may be aluminum, the layer  18  may be titanium, and the layer  20  may be TiO x , where x is between 1 and 2. The TiO x  layer may be evaporated in one embodiment of the present invention.  
         [0015]     Referring to  FIG. 2 , the TiO x  layer  20  may be subjected to an ion implantation indicated as I 1 . The ion implantation species may be germanium in one embodiment. The dose and energy may be optimized to maximize the electrically active defect sites in some embodiments of the present invention. In some cases the energy may be from about 5 to 15 keV with a dose in the range of 1E15 to 1E16 atoms per square centimeter. In general, the implantation conditions may be sufficient to make the TiO x  layer  20  amorphous, in one example.  
         [0016]     The use of ion implantation enhances the performance of TiO x  as the bottom and top electrodes of a polymer memory. The implantation provides the ability modify the work function of the electrode interfaces. It is believed that the modification occurs by introducing vacancies and interstitial defects into the TiO x  layer  20 , that enhance the conductivity by providing sites where electrons and holes can “hop” through the material.  
         [0017]     Referring to  FIG. 3 , the intermediate structure may include a lower electrode made up of layers  16 ,  18 , and  20  patterned into strips through the use of suitable lithography, etch and cleans processes. As a result, between the electrode strips indicated by the presence of the upper TiO x  layer  20 , the insulator  14  is exposed. Thus, a series of parallel strips of lower electrodes are spaced from one another. Many more strips of electrodes may be used in some embodiments.  
         [0018]     Referring to  FIG. 4 , a polymer material  22  may then be deposited over the entire structure, including the lower electrode and the exposed insulator  14 . In one embodiment of the present invention, the polymer material  22  may be spin cast from a solution of a copolymer of vinylidene fluoride (VDF) and trifluoroethylene (TrFE).  
         [0019]     Other ferroelectric or non-ferroelectric polymer materials may be utilized as the material  22  as well, including polyethylene fluoride, copolymers, and combinations thereof, polyacrylonitriles copolymers thereof, and combinations thereof, and polyamides, copolymers thereof, and combinations thereof.  
         [0020]     In some embodiments, the lower TiO x  layer  20  is implanted to enable both upper and lower electrodes to use TiO x  In one embodiment, the lower TiO x  layer  20  is the only implanted layer.  
         [0021]     Referring to  FIG. 5 , thereafter, a second TiO x  layer  24  may be deposited, again using evaporation in one embodiment of the present invention. The layer  24  may then be subjected to a second, optional, ion implantation step. In the case of the implantation I 2 , it is desirable in some embodiments to maximize the number of defects without contaminating (i.e. implanting species into) the polymer layer  22 . This may be done by adjusting the species, dose, and energy. For example, energies of less than 5 keV may be used with a dose in the range of 1E15 to 1E16 atoms per square centimeter and a high atomic mass species such as germanium. The layer  24  may be 200 Angstroms thick in one embodiment.  
         [0022]     As shown in  FIG. 6 , the resulting structure has a second electrode  24  arranged generally transversely to the lower electrode represented by its upper TiO x  layer  20 . As shown in  FIG. 5 , the second electrode  24 , like the lower electrode, may be formed of a stack of layers, including titanium oxide, titanium, and aluminum.  
         [0023]     The upper electrode  24  may be patterned, etched, and photoresist cleaned using any suitable patterning and cleaning processes. Thereafter, additional layers of polymer material and lower and upper electrodes may be stacked on top of the structure shown in  FIG. 6 .  
         [0024]     Turning to  FIG. 7 , a portion of a system  500  in accordance with an embodiment of the present invention is described. The system  500  may be used in wireless devices such as, for example, a personal digital assistant (PDA), a laptop or portable computer with wireless capability, a web tablet, a wireless telephone, a pager, an instant messaging device, a digital music player, a digital camera, or other devices that may be adapted to transmit and/or receive information wirelessly. The system  500  may be used in any of the following systems: a wireless local area network (WLAN) system, a wireless personal area network (WPAN) system, or a cellular network, although the scope of the present invention is not limited to these wireless and/or portable systems or to wireless applications in general.  
         [0025]     The system  500  may include a controller  510 , an input/output (I/O) device  520  (e.g. a keypad, display), a memory  530 , and a wireless interface  540  coupled to each other via a bus  550 . It should be noted that the scope of the present invention is not limited to embodiments having any or all of these components.  
         [0026]     The controller  510  may comprise, for example, one or more microprocessors, digital signal processors, micro-controllers, or the like. Memory  530  may be used to store messages transmitted to or by system  500 . Memory  530  may also optionally be used to store instructions that are executed by the device  510  during the operation of system  500 , and may be used to store user data. Memory  530  may be provided by one or more different types of memory. For example, memory  530  may comprise a volatile memory (any type of random access memory), a non-volatile memory such as a flash memory, a static random access memory and/or a polymer memory of the type illustrated in  FIG. 6 .  
         [0027]     The I/O device  520  may be used to generate a message. The system  500  may use the wireless interface  540  to transmit and receive messages to and from a wireless communication network with a radio frequency (RF) signal. Examples of the wireless interface  540  may include a wireless transceiver or an antenna, such as a dipole antenna, although the scope of the present invention is not limited in this respect.  
         [0028]     While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.