Kurt Hoppe

Metallized Nuclear Tracks in Quasi Metal Oxide Semiconductor Structures for Electronic Devices

The impact of swift heavy ions on silicon oxide and silicon oxynitride on silicon creates etchable tracks in these insulators. After their etching and filling-up with highly resistive matter, these nanometric pores can be used as charge extraction or injection paths toward the conducting channel in the underlying silicon. In this way, a family of electronic structures has been manufactured [German patent: DE 103 25 150 Al (2004), and International patent application: WO 2004/10897 A2 (2004)]. The basic characteristics of these tunable electronic material with pores in oxide on silicon (TEMPOS) structures are summarized. Their functionality is determined by the type of insulator, the etch track diameters and lengths, their areal densities, the type of conducting matter embedded therein, and of course by the underlying semiconductor and the contact geometry. Depending on the TEMPOS preparation recipe and working mode, the structures may resemble gatable resistors, capacitors, diodes, transistors, photocells, or sensors, which renders them rather universally applicable in electronics. TEMPOS structures are sensitive to temperature, light, humidity, and organic gases. Light emitting TEMPOS structures have been produced as well. About 60 TEMPOS-based circuits such as thermosensors, photosensors, humidity and alcohol sensors, amplifiers, frequency multipliers, amplitude modulators, oscillators, and flip-flops have already been designed and successfully tested. Sometimes TEMPOS-based circuits are more compact than conventional electronics.

Tempos structures with gold nanoclusters

Following the preparation of novel electronic MOS-like structures (TEMPOS, tunable electronic material with pores on semiconductors) with Ag-nanocluster (NC)-filled etched ion tracks, Au-nanocluster-filled TEMPOS (Au-NC-TEMPOS) structures are presented in this work. In spite of some similarities, the characteristics of both Ag- and Au-TEMPOS structures differ markedly. This is mainly attributed to the different distributions of the metallic nanoparticles. As in the case of Au-NC-TEMPOS, instabilities show up in their current/voltage characteristics that might be exploited for the construction of electronically active devices.

Swift heavy ion irradiation as a tool for creating novel nanoelectronic structures

An overview is given about the strategies to create a novel ‘Swift-heavy Ion Track Electronics (SITE)’ and an ‘Electrolytic Electronics with Etched Tracks (E3T)’, by combining swift heavy ion tracks in thin insulating membranes with conventional semiconductor-based electronic skills and eventually also with nanoparticles on the one hand, and with electrolytes on the other hand. In this way, novel multiparametric and multilevel ambient-sensing and decision-making electronic elements can be constructed which offer a range of unusual properties. The most interesting feature in both types of ion track electronics is the frequent occurrence of two different working states, eventually leading to negative differential resistances (NDRs). NDRs can show up as well within individual track structures, as via track-to-track interaction; in the latter case, the NDRs are tunable. An interesting consequence of NDRs are self-pulsating tracks. Structures with NDRs are thought to be the primary active elements in both types of electronics. We are now working to improve the reproducibility of these structures, for reliable technological applications.

Resistance of ion track based electronic structures to high voltage and radiation

Recently new electronic structures were introduced which are composed of tunable electronically anisotropic materials deposited onto semiconductors (TEAMS). A subgroup of these TEAMS structures is tunable electronic materials with pores in oxide on semiconductors (TEMPOS), the pores usually being etched ion tracks in silicon oxide filled with (semi)conducting material and the semiconductor substrate usually being of silicon. These structures, especially TEMPOS structures, are expected to be to some extent radiation hard and resistant against high voltage pulses due to their inherent construction principles.In this work, the first test experiments have been undertaken to check this assumption. It has been observed that, indeed, there exist TEAMS structures which are rather stable under severe external influences, but there are also others which are less stable under the same conditions. The degree of hardness against high energy radiation and high voltage electrical pulses appears to depend primarily on the chemical composition of the material embedded in these electronic structures.