Read only memory structure

Details Read only memory structure Read only memory structure

2001-06-25

2003-04-01

Phan, Trong (Department: 2818)

Static information storage and retrieval

Read only systems

C365S100000, C365S148000

Reexamination Certificate

active

06542397

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to semiconductors.
BACKGROUND OF THE INVENTION
A read only memory “ROM”) is a device having a plurality of memory cells that permanently store bits of data. A resistive ROM typically includes a planar array of parallel word lines, which is perpendicular to and insulated from a planar array of parallel bit lines. A designated number of the memory cells in the ROM have a resistive, element connecting a node of one word line with a node of one bit line. The presence or absence of a resistive element in each memory cell determines whether a binary “0” or “1,” for example, is stored therein. The values stored within the ROM are “read” (i.e., output) by measuring a sense current flowing through each bit line from the memory cells of successive word lines.
Various ROM structures are known in the art. One known structure, referred to as a mask-written ROM, employs a semiconductor lithographic mask to “write” (i.e., program) the values of the data bits into the memory cells of the ROM. The mask comprises a pattern for designating each memory cell in which the resistive element is to be fabricated.
With the desired storage capacity (i.e., the number of stored bits per device) of ROMs ever increasing, it follows that the number of cells needed has also been increasing. However, as the number of memory cells increase, the problem of crosstalk has grown. Crosstalk may be characterized as the misinterpretation of the value of bits in adjacent cells being the value of bits stored in cells to be read. Crosstalk results from the influence of the inevitable wire resistance in each bit line. As the number of cells increase, the wire resistance of each bit line increases relative to the resistance of each memory cell. Consequently, an increase in the wire resistance of each bit line increases the likelihood that a substantial portion of the sense current on one word line will be redirected onto an adjacent word line. This may cause the false reading of the binary values stored within each cell of the ROM.
One known approach for minimizing crosstalk has been to incorporate a supplemental resistance—e.g., a field effect transistor—in each memory cell of the ROM. The effective resistance of each cell may therefore be sufficiently increased relative to the wire resistance to reduce the likelihood that substantial amounts of sense current on one word line will be redirected onto an adjacent word line.
As industry drives towards increasing the density (i.e., the number of bits per unit area) of ROMs, however, the use of a field effect transistor as a supplemental resistance has become a problem. Field effect transistors require considerable unit area relative to each ROM cell. Consequently, an alternate ROM structure is needed having a sufficiently high relative memory cell resistance to minimize crosstalk and increase ROM density.
SUMMARY OF THE INVENTION
I have invented a memory structure, such as a ROM, that engenders maximum In density. In my invention, a resistance-altering constituent is disposed within at least one designated memory cell of a plurality of memory cells. More particularly, the resistance-altering constituent may be disposed within a conductive material forming each memory cell of the plurality. Consequently, a first numerical value may be interpreted as being stored in each designated cell and at least a second numerical value may be interpreted as stored in each remaining (non-designated) cell of the plurality. Advantageously, each designated memory cell has a first resistance, while each remaining memory cell has at least a second resistance. I have recognized that disposing the resistance-altering constituent within each designated memory cell sufficiently increases the information storage capability over presently available ROM structures.
In an illustrative example of my invention, each memory cell of the plurality is formed from a conductive layer, such as polycrystalline silicon. Furthermore, hydrogen—a Group 1A element of the Periodic Table—is disposed within the conductive layer of each designated memory cell.
A memory structure embodying the principles of my invention may be advantageously fabricated using the techniques described in my co-pending, commonly assigned, U.S. Patent application, entitled “A METHOD OF VARYING THE RESISTANCE OF A CONDUCTIVE LAYER,” Ser. No. 09/888,879, filed concurrently with the present application on Jun. 25, 2001.


REFERENCES:
patent: 4045310 (1977-08-01), Jones et al.
patent: 4272833 (1981-06-01), Taylor
patent: 4396998 (1983-08-01), Hunt et al.
patent: 4757359 (1988-07-01), Chiao et al.
patent: 4839859 (1989-06-01), Moopenn et al.
patent: 4879587 (1989-11-01), Jerman et al.
patent: 5095362 (1992-03-01), Roesner
patent: 5120679 (1992-06-01), Boardman et al.
patent: 5363329 (1994-11-01), Troyan
patent: 5391518 (1995-02-01), Bhushan
patent: 5394356 (1995-02-01), Yang
patent: 5429975 (1995-07-01), Sheu et al.
patent: 5466963 (1995-11-01), Beasom
patent: 5474948 (1995-12-01), Yamazaki
patent: 5684733 (1997-11-01), Wu et al.
patent: 5696385 (1997-12-01), Song et al.
patent: 5847442 (1998-12-01), Mills et al.
patent: 5859458 (1999-01-01), Hsuch
patent: 5899707 (1999-05-01), Sanchez et al.
patent: 5936880 (1999-08-01), Payne
patent: 5982659 (1999-11-01), Irrinki et al.
patent: 6107666 (2000-08-01), Chang
patent: 6185121 (2001-02-01), O'Neill
patent: 6404665 (2002-06-01), Lowrey et al.
U.S. patent application Ser. No. 09/095,231, Bevk et al., filed Jun. 10, 1998.
U.S. patent application Ser. No. 09/479,708, Mills et al., filed Jan. 7, 2000.

Affiliated with

Also associated with

Rating

Read only memory structure does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Read only memory structure, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Read only memory structure will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3087308