Abstract:
The present invention includes an address decoder for a memory device. The address decoder includes a number of address lines and a number of output lines. The address lines, and the output lines form an array. A number of non-volatile memory cells are disposed at intersections of output lines and address lines. Each non-volatile memory cell includes a metal oxide semiconductor field effect transistor (MOSFET), a stacked capacitor formed according to a dynamic random access memory (DRAM) process, and an electrical contact that couples the stacked capacitor to a gate of the MOSFET. The non-volatile memory cells are selectively programmed such that the non-volatile memory cells implement a logic function that selects an output line responsive to an address provided to the address lines. 
     Methods, integrated circuits, and electronic systems are similarly provided and included within the scope of the present invention.

Description:
RELATED APPLICATIONS 
     This application is related to the co-filed and commonly assigned applications, Ser. No. 09/259,493, entitled “Dram Technology Compatible Non-volatile Memory Cells,” by Wendell P. Noble and Eugene H. Cloud, Ser. No. 09/261,597, entitled “Applications for Dram Technology Compatible EEPROM Cells,” by Eugene H. Cloud and Wendell P. Noble, and Ser. No. 09/261,479, entitled “Construction and Applications for Non-volatile Reprogrammable Switches,” by Wendell P. Noble and Eugene H. Cloud which are hereby incorporated by reference and filed of even date herewith. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to semiconductor integrated circuits and, more particularly, to DRAM technology compatible processor/memory chips. 
     BACKGROUND OF THE INVENTION 
     Many products need various amounts of memory. Two of the most useful types of memory are high speed, low cost memory typically implemented as Dynamic Random Access Memory (DRAM) and non-volatile memory typically implemented as Electrically Erasable and Programmable Read Only Memory (EEPROM) or Flash memory. The ability to combine DRAM and EEPROM styles of memory, as well as logic and data processing functions implemented by Programmable Logic Arrays (PLA&#39;s) especially if little or no additional manufacturing complexity is required, would allow a number of cost effective applications that do not currently exist or that, heretofore were too costly to be commercially viable. 
     With the increasing array density of successive generations of DRAM chips, the attractiveness of merging other functions onto the chip also increases. However, any successful merged technology product must be cost competitive with the existing alternative of combining separate chips at the card or package level, each being produced with independently optimized technologies. Any significant addition of process steps to an existing DRAM technology in order to provide added functions such as high speed logic, SRAM or EEPROM becomes rapidly cost prohibitive due to the added process complexity cost and decreased yield. Thus, there is a need for a means of providing additional functions on a DRAM chip with little or no modification of the DRAM optimized process flow. 
     Among the desired additional functions, EEPROM is one for which the differences between the separately optimized technologies is the greatest. The typical EEPROM cell consists of a MOSFET with two stacked gates, a floating gate directly over the device channel and a control gate atop and capacitively coupled to it. 
     It would be very desirable to reduce all the major elements of a PC on to a single chip, including CPU, memory and input/output. While at the present time it may not be possible to make a whole PC on a single die, many processor like functions might most conveniently be embedded on the DRAM die. PLAs on a DRAM die would be well suited for memory address correction/repair by changing the addresses to remove faulty rows/columns, and replace them with functional ones. An example of a redundancy repair scheme is shown in U.S. Pat. No. 5,324,681 issued Lowrey on Jun. 28, 1994. Another is provided in U.S. Pat. No. 4,051,354 issued Choate on Sep. 27, 1997. Another is provide in U.S. Pat. 5,327,380 issued Kersh III on Jul. 5, 1994. None of these, however, incorporate an optimized DRAM technology process flow. PLAs on a DRAM die would also be desirable for use as dedicated processors embedded on the DRAM chip. 
     Recent publications outline the problems in trying to embed DRAMs in high performance ULSI logic. The conclusions are that because of the height differences between conventional stacked capacitor DRAM cells and high performance logic circuits that this can only be reasonably accomplished with trench capacitor DRAMS. 
     Modern DRAM technologies are driven by market forces and technology limitations to converge upon a high degree of commonality in basic cell structure. For the DRAM technology generations from 4 Mbit through 1 Gbit, the cell technology has converged into two basic structural alternatives; trench capacitor and stacked capacitor. A method for utilizing a trench DRAM capacitor technology to provide a compatible EEPROM cell has been described in U.S. Pat. No. 5,598,367. A different approach is needed for stacked capacitors however. 
     Thus, there is a need for merging processor and memory functions on a single DRAM chip. Similarly, there is a need for using PLAs on a DRAM chip as decoder devices. It is desirable that such processor/PLA capability be fabricated onto the DRAM chip with little or no modification of the DRAM optimized process flow. 
     SUMMARY OF THE INVENTION 
     The above mentioned problems for merging processor/PLAs and memory functions on a single DRAM chip as well as other problems are addressed by the present invention and will be understood by reading and studying the following specification. The present invention includes a compact non-volatile memory cell structure formed using a DRAM process technology. 
     The present invention includes a programmable logic array having a first logic plane that receives a number of input signals. The first logic plane has a plurality of non-volatile memory cells arranged in rows and columns that are interconnected to provide a number of logical outputs. A second logic plane is provided which has a number of non-volatile memory cells arranged in rows and columns that receive the outputs of the first logic plane and that are interconnected to produce a number of logical outputs such that the programmable logic array implements a logical function. Each non-volatile memory cell includes a metal oxide semiconductor field effect transistor (MOSFET). Each non-volatile memory cell includes a stacked capacitor formed according to a dynamic random access memory (DRAM) process. And, each non-volatile memory cell includes an electrical contact that couples the stacked capacitor to a gate of the MOSFET. 
     Another embodiment of the present invention includes an address decoder for a memory device. The address decoder includes a number of address lines and a number of output lines. The address lines, and the output lines form an array. A number of non-volatile memory cells are disposed at intersections of output lines and address lines. Each non-volatile memory cell includes a metal oxide semiconductor field effect transistor (MOSFET), a stacked capacitor formed according to a dynamic random access memory (DRAM) process, and an electrical contact that couples the stacked capacitor to a gate of the MOSFET. The non-volatile memory cells are selectively programmed such that the non-volatile memory cells implement a logic function that selects an output line responsive to an address provided to the address lines. 
     These and other embodiments, aspects, advantages, and features of the present invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art by reference to the following description of the invention and referenced drawings or by practice of the invention. The aspects, advantages, and features of the invention are realized and attained by means of the instrumentalities, procedures, and combinations particularly pointed out in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view illustrating in detail the make up of each non-volatile memory cell according to the teachings of the present invention. 
     FIG. 2 is a simplified block diagram of a field programmable logic array (PLA) according to the teachings of the present invention. 
     FIG. 3 is a schematic diagram illustrating generally an architecture of one embodiment of a progammable logic array (PLA) constructed according to the teachings of the invention. 
     FIG. 4 is a schematic diagram illustrating generally an architecture of one embodiment of a programmable decoder according to the teachings of the present invention. 
     FIG. 5 illustrates application of programmed logic arrays (PLA&#39;s), formed according to the teaching of the present invention, embedded processor on a DRAM die. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following detailed description of the invention, reference is made to the accompanying drawings which form a part hereof, and in which is shown, by way of illustration, specific embodiments in which the invention may be practiced. In the drawings, like numerals describe substantially similar components throughout the several views. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the present invention. The terms wafer and substrate used in the following description include any structure having an exposed surface with which to form the integrated circuit (IC) structure of the invention. The term substrate is understood to include semiconductor wafers. The term substrate is also used to refer to semiconductor structures during processing, and may include other layers that have been fabricated thereupon. Both wafer and substrate include doped and undoped semiconductors, epitaxial semiconductor layers supported by a base semiconductor or insulator, as well as other semiconductor structures well known to one skilled in the art. The term conductor is understood to include semiconductors, and the term insulator is defined to include any material that is less electrically conductive than the materials referred to as conductors. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled. 
     FIG. 1 is a perspective view illustrating in detail the make up of the non-volatile memory cell, e.g.  100 , according to the teachings of the present invention. The non-volatile memory cell  100  includes all the embodiments of the non-volatile memory cell structure presented and described in detail in the co-filed application Ser. No. 09/259,493, entitled “DRAM Technology Compatible Non-volatile Memory Cells,” by Wendell P. Noble and Eugene H. Cloud, which is hereby incorporated by reference in its entirety. 
     As shown in FIG. 1, the non-volatile memory cell structure  100  includes a MOSFET  110  and a capacitor  120  fabricated using conventional DRAM process steps. In one embodiment, the MOSFET  110  includes an n-channel metal oxide semiconductor (NMOS) transistor  110  formed in a semiconducting substrate  111 . The MOSFET  110  includes a gate  112  separated by a gate oxide  113  from a channel region  114  of the MOSFET  110 . In one embodiment, the gate oxide  113  has a thickness of less than 100 Angstroms (Å) and acts as a tunneling oxide. Gate  112  includes a polysilicon gate  112 , a polycide gate  112 , salicided gate structure; or other conductive gate material as known to one of ordinary skill in the art of DRAM transistor fabrication. The channel region  114  couples a first diffused region  115  to a second diffused region  116 . The DRAM transistor is formed according to a conventional, DRAM optimized process flow, as is known to those of ordinary skill in the art of DRAM chip fabrication. 
     As shown in FIG. 1, the capacitor  120  is formed in a subsequent layer above the MOSFET  110 . The capacitor  120  is separated from the MOSFET  110  by an insulator layer  132 . Capacitor  120  includes a bottom plate  121  and a top plate  123 , or a control gate  123  which is separated from the bottom plate  121  by a dielectric layer or capacitor dielectric  122 . The bottom plate  121  serves as a storage node  121  and the top plate serves as a plate capacitor  123  for the capacitor  120 . The bottom plate  121  comprises a floating gate  121  for the non-volatile memory cell  100  which is connected through insulator layer  132  to gate  112  by an electrical contact  130 . In one embodiment, the entire stack  121 ,  130  and  112  serves as a floating gate. The top plate  123  comprises a control gate  123  for the non-volatile memory cell  100 . 
     In one embodiment, shown in FIG. 1, capacitor  120  includes a stacked capacitor which is cup shaped  120 . The bottom plate  121  has interior walls  121 A and exterior walls  121 B. The capacitor dielectric  122  is conformal to the interior walls  121 A and the exterior walls  121 B of the bottom plate  121 . The top plate  123  is conformal to the capacitor dielectric  122 . A portion of the top plate  123  is located within and opposes the interior walls  121 A of the bottom plate  121 , separated therefrom by the capacitor dielectric  122 . A portion of the top plate  123  is locate outside of and opposes the exterior walls  121 B of the bottom plate  121  separated therefrom by the capacitor dielectric  122 . In one embodiment, the capacitor dielectric has a thickness of less than the equivalent of 100 Angstroms (Å) of SiO 2 . As one of ordinary skill in the art will understand upon reading this disclosure, other of stacked capacitor  120  configurations, such as domes or flat plates, are applicable. To create an array of such cells, such as shown in the co-filed application Ser. No. 09/259,493, entitled “DRAM Technology Compatible Non-volatile Memory Cells,” by Wendell P. Noble and Eugene H. Cloud, bit lines are connected to the first and second diffused regions,  115  and  116 . For minimum cell size, the bit lines may consist of diffusion lines which traverse the array. By then patterning the top plate  123  of the stacked capacitor  120  into strips orthogonal to the diffused bit lines, control gate  123  word lines couple to the bottom plate  121  and the MOSFET  110  of the non-volatile memory cell  100  structure. 
     The resulting non-volatile memory cell  100  has the same physical and electrical features as conventional non-volatile memory cells and thus conventional methods of programing (e.g. channel hot electron “CHE” injection) and erasure (e.g. Fowler Nordheim “F-N” tunneling) may be used. However, whereas conventional non-volatile memory cells have capacitive coupling ratios of 0.6 to 1.0, as defined in the co-filed application Ser. No. 09/259,493, entitled “DRAM Technology Compatible Non-volatile Memory Cells,” by Wendell P. Noble and Eugene H. Cloud, the inherently high stacked capacitor  120  surface area of the present invention can provide coupling ratios many times this. Therefore the gate voltage swings needed for programming and erasure are greatly reduced. 
     FIG. 2 is a simplified block diagram of a field programmable logic array (PLA)  200  according to the teachings of the present invention. PLA  200  includes two major constituents: a first logic plane  220  and a second logic plane  230 . The first and second logic planes  220  and  230  are formed using an array of non-volatile memory cells  100  as presented and described in detail in connection to FIG.  1 . In one embodiment, the first and second logic planes  220  and  230  each comprise NOR logic circuits such that PLA  200  implements NOR-NOR logic. In other embodiments, first and second logic planes  220  and  230  are constructed from arrays of non-volatile memory cells  100  that are configured to implement AND-OR, OR-AND, NAND-NAND, NOR-OR, OR-NOR, AND-NOR, and NAND-AND logic. 
     Input lines  225  are coupled to. receive a number of input signals. Inverters/drivers  250  are coupled to the input lines  225  such that first logic plane  220  is capable of receiving each of the input signals and their complements. First logic plane  220  produces a number of output signals that are logical combinations of the signals from inverters/drivers  250 . The output signals from first logic plane  220  are provided to second logic plane  230  via interconnection lines  222 . Second logic plane  230  produces a number of output signals that are logical combinations of the signals from interconnection lines  222 . 
     In addition, various control circuits and signals not detailed herein initiate and synchronize the PLA  200  operation as known to those skilled in the art. The PLA  200  implementation described with respect to FIG. 2 is illustrative only and is not intended to be exclusive or limiting. 
     FIG. 3 is a schematic diagram illustrating generally an architecture of one embodiment of a programmable logic array (PLA), indicated generally at  300 , and constructed according to the teachings of the present invention. PLA  300  implements an illustrative logical function using a two level logic approach. Specifically, PLA  300  includes first and second logic planes  310  and  320 . In this example, the logic function is implemented using NOR-NOR logic. First and second logic planes  310  and  320  each include an array of non-volatile memory cells  100 , as presented and described in detail in connection to FIG. 1, that are configured to implement the logical function of PLA  300 . 
     It is noted that the configuration of FIG. 3 is provided by way of example and not by way of limitation. Specifically, the teachings of the present application are not limited to programmable logic arrays in the NOR-NOR approach. Further, the teachings of the present application are not limited to the specific logical function shown in FIG.  3 . Other logical functions can be implemented in a programmable logic array with non-volatile memory cells  100  using any one of the various two level logic approaches. 
     First logic plane  310  receives a number of input signals at input lines  312 . In this example, no inverters are provided for generating complements of the input signals. However, first logic plane  310  can include inverters to produce the complementary signals when needed in a specific application. 
     First logic plane  310  includes a number of non-volatile memory cells  100  that form an array. The non-volatile memory cells  100  are located at the intersection of input lines  312 , and interconnect lines  314 . Not all of the non-volatile memory cells  100  are operatively conductive in the first logic plane. Rather, the non-volatile memory cells  100  are selectively programmed to respond to the input lines  312  and change the potential of the interconnect lines  314  so as to implement a desired logic function. Thus, some non-volatile memory cells  100  are left unprogrammed. This selective interconnection is referred to as programming since the logical function implemented by the programmable logic array is enterred into the array by the non-volatile memory cells  100  that are used at the intersections of input lines  312 , and interconnect lines  314  in the array. 
     In this embodiment, each of the interconnect lines  314  acts as a NOR gate for the input lines  312  that are connected to the interconnect lines  314  through the non-volatile memory cells  100  of the array. For example, interconnection line  314   a  acts as a NOR gate for the signals on input lines  312   a ,  312   b  and  312   c . That is, interconnect line  314   a  is maintained at a high potential unless one or more of the non-volatile memory cells  100  that are coupled to interconnect line  314   a  are turned on by a high logic level signal on one of the input line  312 . When a control gate address is activated, through input lines  312 , each non-volatile memory cell  100  either conducts or does not conduct depending on the charge stored upon its floating gate, this performs the NOR positive logic circuit function, an inversion of the OR circuit function results from inversion of data onto the interconnect lines  314  through the non-volatile memory cells  100  of the array. The sense amplifiers  316  at the ends of the interconnect lines  314  are used as amplifiers and drivers for the passing data into the second array  320 . In this manner a NOR-NOR is most easily implemented utilizing the normal DRAM array structure, only the function of devices is changed. 
     In a similar manner, second logic plane  320  comprises a second array of non-volatile memory cells  100  that are selectively programmed to provide the second level of the two level logic needed to implement a specific logical function. In this embodiment the array of non-volatile memory cells  100  is also configured such that the output lines  318  comprise a logical NOR function of the signals from the interconnection lines  314  that are coupled to particular output lines through the non-volatile memory cells  100  of the second logic plane  320 . 
     FIG. 4 is a schematic diagram that illustrates one embodiment of a decoder, indicated generally at  400 , that is constructed according to the teachings of the present invention. Decoder  400  can be used, for example, as a memory address decoder such as a column decoder or a row decoder. 
     Decoder  400  of FIG. 4 includes a number of non-volatile memory cells, e.g.  435 , as described in detail in connection with FIG.  1 . The number of non-volatile memory cells are formed at the intersection of output lines O 1  through O 4  with either an address line A 1  through A 3  or inverse address line {overscore (A)} 1  through {overscore (A)} 3 . The inverse address lines are coupled to associated address lines through an inverter as shown. For example, non-volatile memory cell is located at the intersection of address line A 1  and output line O 1 . Decoder  400  is programmed and reprogrammed according to the techniques generally know for programming conventional non-volatile memory cells. Any selected number of the non-volatile memory cells be operatively coupled to the address lines, A 1  through A 3 , inverse address lines, {overscore (A)} 1  through {overscore (A)} 3 , or the output lines, O 1  through O 4 . In this manner, the number of non-volatile memory cells are selectively programmed into the array in order to implement a desired logical function. 
     In this embodiment of FIG. 4, each of the output lines, O 1  through O 4 , implements a NOR logic function for the address lines, A 1  through A 3 , and inverse address lines, {overscore (A)} 1  through {overscore (A)} 3 , that are connected to it through the vertical transistors. For example, output line O 1  is coupled to the drains of non-volatile memory cells  435 ,  436 , and  437 . Non-volatile memory cells  435 ,  436 , and  437  have gates, as shown in detail in FIG. 1, that are coupled to receive signals from address lines A 1 , A 2 , and A 3 , respectively. Output line O 1  produces the logical NOR of the logic values provided on address lines A 1 , A 2 , and A 3 . Output line O 1  produces a low logic level when any one of the address lines A 1 , A 2 , and A 3  is brought to a high logic level and the floating gate on an associated non-volatile memory cell, as shown in detail in FIG. 1, is absent of charge (e.g. in an unprogrammed state). Further, output line O 1  produces a high logic level only when the address lines A 1 , A 2 , and A 3  are all at a low logic level. 
     The remaining output lines are selectively coupled to other non-volatile memory cells as shown to implement additional NOR functions. These NOR functions are chosen such that the input address lines, A 1 , A 2 , and A 3 , (and inverse address lines, {overscore (A)} 1 , {overscore (A)} 2 , {overscore (A)} 1 ) can be used to selectively address the output lines, O 1  through O 4 . It is noted that the logical functions implemented in array  400  are shown by way of illustration and not by way of limitation. Other logical functions can be implemented without departing from the spirit and scope of the present invention. 
     Generally speaking, decoder  400  can be fabricated with N address input lines to uniquely select 2 N  output lines. Thus, in an alternative embodiment, two address lines, A 1  and A 2 , are used to selectively access four output lines, O 1  through O 4 . In this embodiment, the purpose of address line A 3  is to hold the output lines at a low level when an address signal has not yet been received. 
     FIG. 5 illustrates application of PLA&#39;s, structure according to the teachings of the present invention, as an embedded processor on a DRAM die  500 . In the embodiment shown in FIG. 5, data from the DRAM memory arrays  510  is input to the processor  520  at the top of the FIG. 5 via interconnect lines  512 . At the end of the processing, as defined by the program selected for data processing from the program circuit  540 , processed data is sent back for storage in the DRAM arrays  510  from a data output circuit  530  via interconnect lines  514 . In one embodiment of FIG. 5, the individual cell type for implementation of a particular processor  520  function includes a program stored in the program circuit  540  using EEPROM cells. Memory is held in the memory arrays  510  and registers  590  using conventional DRAM cells. In this embodiment, the individual cell type for implementation of the particular processor  520  function includes a function and sequence circuit  550 , FLAGS  560 , one or more serial adders  570 , and a data selector  580  using PLAs constructed according to teachings of the present invention. As is shown in FIG. 5, most functions in the processor can be implemented using PLA&#39;s according to the teachings of the present invention. 
     CONCLUSION 
     Thus, the ability to provide processor/PLA capability on a DRAM chip according to a DRAM optimized process flow has been shown by the present invention. This disclosure provides not only a technique for combining logic (implemented with PLA&#39;s) with stacked capacitor DRAM cells but also describes the alternative approach to improving system performance, namely “embedded logic in DRAMs”, not DRAMs embedded in logic. 
     The ability to process data stored on the DRAM die allows a number of cost effective applications that do not currently exist or that, heretofore were to costly to be commercially viable. It is particularly suited to processing data which requires a large number of parallel operations. The use of programmable embedded processors avoids the necessity of transferring intermediate data on and off chip through input/output drivers and circuits and greatly speeds data processing. This aids in applications such as a dedicated signal processor in which data may be loaded in to a range of DRAM addresses and then having an algorithm such as the Fast Fourier Transform (FFT), performed on the data with the results stored in another range of DRAM memory all on the same chip. The user application can retrieve the resultant processed data from the memory. The ability of an on chip non-volatile memory means that the processor program instructions, implementing various algorithms, can not only be stored on the die but also can be easily changed to suit a variety of applications. The PLA&#39;s of the present invention allow powerful techniques for data processing which are especially useful for parallel data processing applications such as image processing or general Digital Signal Processing (DSP). The PLA&#39;s of the present invention are also suitable for making general purpose processors embedded in a DRAM by which one could emulate a general purpose processor such as an 80C251, an 8 bit general purpose microprocessor. Here, 5-10 Mbits of the DRAM of the DRAM chip can be configured for PLA&#39;s, non-volatile storage, and where DRAM serves as registers. 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.