Anodization of Ti by high electric fields at the tip of a scanned probe can be used to produce nanoscale features consisting of oxides of Ti. In this manner, Ti can be used as a sacrificial resist for nanoscale lithography by exploiting the etching selectivity differences between Ti and anodized Ti. The anodization was accomplished with an atomic force microscope using Ticoated silicon nitride cantilevers. The anodizing bias voltage is applied to the tip and is independent of the feedback, unlike the scanning tunneling microscope. With this setup we were able to fabricate sub-40 nm lines by direct anodization of Ti. It is also shown that once tip and sample are brought into hard contact, subsequent bending of the cantilever has little effect on the linewidth or thickness of the anodized material.

The direct modification of silicon and other semiconductor and metal surfaces by the process of anodization using the electric field from a scanning probe microscope in conjunction with the absorbed water from the atmosphere as the electrolyte is one promising method of accomplishing direct write lithography for the electron device fabrication using scanning probe microscopes. Both scanning tunneling microscopes and conductive-tip atomic force microscopes have been used for anodization with the work reported here primarily accomplished with a conductive-tip atomic force microscope. We have found that the terminating thickness of the scanning probe microscope induced oxide is governed by the diffusion limited electric field at the surface ͑which in this case is a function of the scanning probe microscope tip potential͒, with many similarities to liquid electrolyte anodization process. In particular, when using atmospheric water as the electrolyte on a silicon substrate and a conductive-tip atomic force microscope with a Ϫ7 to Ϫ10 V tip potential, the terminating electric field that is reached as the silicon dioxide thickness increases is to its final value of 80 Å is ϳ1ϫ10 7 V/cm. This is consistent with the diffusion limited electric field that is observed in many other anodization processes and the native oxidation of silicon ͑Mott-Cabrera process͒.

A new switching mechanism in a two-terminal semiconductor heterolayer structure is proposed which capitalizes on nonlinear electron temperature effects in adjacent heterolayers. The estimated switching speed of an optimized heterostructure hot electron diode should be extremely fast, perhaps as fast as 200 fs. Data are presented on prototype devices which show the expected negative differential resistance and indicate that the basic physical model is correct.

Ultrahigh purity (UHP) silicon nitride (Si3N4) was applied as a barrier layer to reduce the reaction of high-k materials with the underlying silicon channel. UHP Si3N4 was grown by rapid thermal nitridation (RTN) in chemically scrubbed ammonia in an ultrahigh vacuum (UHV) chamber. The grown thickness nearly saturates for nitridation times greater than 10 s. This self-limiting thickness increases by about 0.2 nm per 100 °C nitridation temperature from 500 to 900 °C. In situ Auger show that UHP nitride has less than 1% oxygen contamination. The effective charge density of UHP Si3N4 was found to increase with the thickness of nitride layer. The thinnest nitride layers (0.5 nm) have a charge density of approximately 5×1011 cm−2. The peak mobility of field effect transistors made from such a layer are 180 cm2/V s (n channel) and 50 cm2/V s (p channel). Both are about 70% of the value predicted by the universal curve.

Articles you may be interested inRoom-temperature negative differential resistance in polymer tunnel diodes using a thin oxide layer and demonstration of threshold logic Appl. Phys. Lett. 87, 203506 (2005); 10.1063/1.2130395Voltage switching and oscillations in a single barrier heterostructure hot-electron diode