Contents 1. Introduction 2. General behavior of m e m o r y switching MZM diodes 2.1 The MIM diode familyconfigurations and materials 2.2 I-U characteristics and switching 2.3 Different models describing switching 3. MZM diodes w i t h carbonaceous current paths 3.1 Definition of the particular class 3.2 Basic and adsorption-assisted electroforming 3.3 Current-voltage behavior 3.4 Bistable statesthe OFF and ON state conduction 3.5 Electron microscopical search for the current paths 3.6 Localizing the voltage drop in planar MIM diodes 4. External influences on switching 4.1 Studies of the regeneration processa two-stage mechanism 4.2 Search for the adsorbed species 4.3 Influence of partial pressure and residual gas composition on regeneration 4.4 Influence of gases with electronegative molecules 4.5 Influence of passive gas species on regeneration 4.6 Charged particle induced off switching 4.7 Can metal re-covering cause regeneration ' 2 5 . Memory effects and material inflzie~zce 5.1 Memory states 5.2 The regeneration threshold voltage 5.3 Material parameters and long-term stability l ) Schlol3gartenstr. 7, D-6100 Darmstadt, FRG. H. PACNIA and N. SOTNIH 6. Emission phenomena 6.1 Electron emission 6.2 Photon emission spectra 6.3 Correlation between switching events of the circulating current and the emis-6.4 Voltage pulse experiments sion processes 7 . Conclusions
7.1What is known about the carbonaceous filament switches ? 7.2 Application aspects and an outlook References the (closed) sandwich configuration. The whole structure is ope11 and directly accessible to the environmental gas atmosphere or the vacuum, which strongly affects the switching behavior. These structures are suitable also for electron microscope investigations. Of course, these advantages made i t possible to enlarge the state of information of the fundamental mechanisms significantly. Therefore, conclusions in this review shall mainly be based on results from planar diodes, not neglecting those from sandwich ones if suitable.
General Behavior of Memory Switching MIM Diodes
The MZM diode familyconfigurations and materialsThe usual method t o prepare a sandwich diode (Fig. l a ) is first to deposit a metal (or any other conductor) stripe on an insulating substrate (frequently of glassy consistence). This may be either oxidized or covered with an insulator (or any low conducting) material of thickness 5 nm to 1 pm (we shall not treat thinner samples,
