Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1999-11-24
2001-11-27
Thomas, Tom (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S295000, C257S306000
Reexamination Certificate
active
06323513
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention lies in the field of semiconductor technology and relates to a semiconductor component having at least one capacitor. The capacitor has a metal oxide layer between a first and a second electrode. A remanent electrical polarization can be generated in the metal oxide layer by supplying a given voltage difference between the first and second electrodes.
Among other memory devices, so-called nonvolatile memories are proposed for future generations of semiconductor memories. In these nonvolatile memories, the individual memory cells each include a capacitor having a ferroelectric layer as the capacitor dielectric. In this layer, a remanent polarization of the ferroelectric material can be brought about by applying an electric field. It is thus possible to store information in the capacitor depending on the direction of the polarization. Since, unlike in the so-called DRAMs, the information is not stored by accumulated charges, there is also no risk of self-discharge of the capacitor and thus there is no risk of the information disappearing. The polarization produced in the ferroelectric is preserved, in principle, for an infinite time period, which is why such memories are also called nonvolatile memories.
A semiconductor component of the type mentioned above and which contains nonvolatile memory elements is described in U.S. Pat. No. 5,615,144, for example. The memory cells disclosed therein each include a ferroelectric capacitor, one of whose two electrodes is connected to a bit line via a selection transistor. The other electrode is connected to a so-called plate line on which a pulse signal is present. With the selection transistor open, one electrode of the capacitor is brought to the potential of the bit line that is now connected to it. Depending on the signals on the bit line and plate line, the electric field acting on the capacitor dielectric is altered and the orientation and level of the remanent polarization are thus affected.
With the selection transistor closed, one electrode of the capacitor is disconnected from the bit line. It has been shown, however, that this capacitor electrode is electrostatically charged relative to the other electrode as a result, for example, of leakage currents from adjacent cells or of the closed selection transistor, and can thus contribute to an undesired erasure of the polarization or polarization reversal of the capacitor dielectric. This however leads to an irreversible loss of data which must be avoided.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a semiconductor component which overcomes the above-mentioned disadvantages of the heretofore-known components of this general type and in which undesired alterations or changes of the stored information are avoided. It is furthermore an object of the invention to provide a method for fabricating a semiconductor component of this type.
With the foregoing and other objects in view there is provided, in accordance with the invention, a semiconductor component, including a capacitor having a first electrode, a second electrode, and a metal oxide layer disposed between the first electrode and the second electrode, the metal oxide layer having a first resistance and being remanently electrically polarizable by a given voltage difference between the first electrode and the second electrode; and a resistance element disposed at the capacitor and electrically connecting the first electrode to the second electrode, the resistance element having a second resistance smaller than the first resistance.
In the case of a semiconductor component of the type mentioned above, the first-mentioned object is achieved according to the invention by providing at least one resistance element at the capacitor. The resistance element electrically connects the first electrode to the second electrode and has a predetermined resistance or resistance value, which is lower than the resistance of the metal oxide layer.
The basic concept of the invention is to connect a defined short-circuiting element parallel with the capacitor so that accumulated charges can flow away via this element and, consequently, a potential equalization is brought about between the two capacitor electrodes. The predetermined resistance of the resistance element or of the short-circuiting element should in this case be dimensioned such that, on the one hand, the desired bringing about of the polarization in the event of the addressing of the capacitor is impeded only to an insignificant extent and, on the other hand, a sufficient potential equalization can be effected in the event of a non-addressing. The level of the resistance of the resistance element must therefore be determined by an overall consideration of the electrical circuit that is realized. An essential aspect in this case is that in the event of the remanent polarization being written in, the required voltage is dropped virtually completely across the capacitor and the resistance element, which is connected in parallel with the capacitor. In other words, the total resistance formed from these two elements is still considerably higher than the sum of all the line resistances and of the transistor resistance (with the transistor open). Thus, the resistance element must be dimensioned in such a way that the voltage pulse for bringing about the remanent polarization, as seen over its entire time duration, leads to an electric field which acts effectively on the capacitor dielectric and suffices to bring about a remanent (residual, permanent) electrical polarization in the capacitor dielectric.
On the other hand, the resistance of the resistance element should be low enough to enable the potential equalization of the two electrodes of the capacitor in the event of an unintentional charging of the first and second electrodes relative to one another. Since electrostatic charging of the electrodes, in contrast to the time duration of the preselected voltage difference for bringing about the remanent electrical polarization, takes place essentially significantly more slowly, the magnitude of the resistance of the resistance element can be calculated relatively easily with regard to the required conditions. Thus, this resistance should be lower than the resistance of the metal oxide layer and enable the capacitor to be discharged with a time constant which is at least ten times longer than the time duration for bringing about the remanent polarization. An expedient magnitude of the resistance of the resistance element lies approximately between 1 M&OHgr; and 100 G&OHgr;, a magnitude between 10 M&OHgr; and 100 M&OHgr; being preferred.
In the case of a plurality of memory cells, for example in the case of ferroelectric RAMs, each memory cell preferably has its own resistance element. This assignment is also expedient in the case of memory cells in which the second electrodes are formed by a common metal layer.
In a preferred embodiment, the resistance element is fabricated from polysilicon or from a conductive nitride or silicide, for example a metal silicide. In this case, the resistance of the resistance element, that is to say its effective overall or total resistance, can be set by a suitable doping and/or suitable geometrical dimensioning (effective cross sectional area).
The resistance element is preferably configured as a self-aligned lateral edge web or edge layer on at least one side area or side face of the metal oxide layer. In a further preferred embodiment, the resistance element is formed by a contact hole filled with conductive material in the metal oxide layer. A further possibility for forming a resistance element is to form the resistance element from a layer made of conductive material which covers the entire top side of the first electrode. At least on a side area or side face of the first electrode, this layer covers the second electrode which is applied at the side area with the metal oxide layer being interposed.
In the aforementioned preferred exemplary embodiments, th
Hartner Walter
Schindler Gunther
Greenberg Laurence A.
Infineon - Technologies AG
Lerner Herbert L.
Nguyen Cuong Q
Stemer Werner H.
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