Computing apparatus comprising a programmable resistor

DETAILED DESCRIPTION OF SOME PREFERRED EMBODIMENTS A distinguishing characteristic of computing apparatus according to the invention is the use of one or more programmable resistor bodies.
In such a body the resistance of a given predetermined region can be set to substantially any resistance value (within a given resistance range) by means of an appropriate electrical "write" signal, and can be reset to the original high resistance state, or to some intermediate resistance state, by means of an appropriate electrical "erase" signal.
Typically, the "write" signal comprises one or more pulses of one polarity (of amplitude, e.
g.
, in the range 1-5 volt), and the "erase" signal comprises one or more pulses of the opposite polarity (e.
g.
, also of amplitude in the 1-5 volt range).
Both (or either) of the signals may also comprise an approprate DC bias voltage.
The "resistors" (i.
e.
, the portions of material associated with any given pair of S.
sub.
i and S.
sub.
j) are formed in a matrix of an appropriate relatively high resistivity material.
The material can be monocrystalline, polycrystalline, or amorphous, and frequently is an inorganic oxide.
In currently preferred embodiments, the programmable resistor body is a thin layer of material that was deposited by a known technique (e.
g.
, sputtering) on an appropriate substrate (e.
g.
, an insulator such as Al.
sub.
2 O.
sub.
3).
The programmable resistor body typically is an appropriately doped insulator.
Individual members of the dopant species will be referred to as "ions", without intending to thereby limit the nature of possible dopants.
For instance, "ions" is intended to include crystal defects such as vacancies.
The doping level is chosen such that, for randomly distributed dopant ions, the room temperature resistivity of the doped material is still relatively high.
It is generally desirable that the ratio between maximum resistance (R.
sub.
off) and minimum resistance (R.
sub.
on) be at least 10.
sup.
2 and preferably be of order 10.
sup.
3 or even larger