Davide Patti

Dovetail Tip: A New Approach for Low-Threshold Vacuum Nanoelectronics

An innovative approach for the fabrication of low-threshold, nanoscale field-emitter cathodes and arrays is proposed. By shaping a titanium cathode as dovetail geometry and using a thin vertical wall of high-permittivity dielectric, Si3N4, to isolate the tip from the gate, the electric field intensity near the tip edges is strongly increased, and a turn-ON voltage in the range of a few volts is predicted numerically and observed experimentally. The resulting cathode structure is compact, self-aligned to the vacuum cavity and is fabricated through the standard silicon fabrication processes. Besides, unlike all existing approaches, vacuum is achieved at the wafer level and not at the package level, thereby reducing fabrication costs. Measurements on a first prototyped array of 5×4 diode-connected parallel devices with a silicon area of 5 μm×4 μm, confirm Fowler-Nordheim emission with a 2 V turn-ON voltage, while displaying a total emission current of 25 μA at a gate-cathode bias of 20 V.

Estimation of in-cylinder pressure using spark plug discharge current measurements

In-cylinder pressure of spark ignition engines is correlated with several variables of the compression, injection, and ignition processes. Therefore, by monitoring the pressure of each cylinder we can improve the electronic engine supervision and control in terms of fast response and accuracy, thus enabling online diagnosis and overall efficiency improvement. However, the pressure measurement methods proposed until now have not been generally accepted at the production level due to their cost and/or complexity. In this paper we describe a novel approach that derives the pressure information from the measurement of the ordinary spark plug discharge current. In this manner, the mechanical part of the engine does not require substantial modification. To demonstrate the viability of the proposed technique, a prototype measurement system was set up and tested. Preliminary experimental data show that pressure in stationary conditions can be estimated with an error lower than 5% for pressure above 3 atmospheres.

Silicon p–n junctions biased above breakdown used as monitors of carrier lifetime

In this paper we show that single-photon avalanche detectors (SPADs) may have a strong potential as very sensitive on-wafer tools for lifetime monitoring, given their simple fabrication process and their straightforward use in the measurements. We have fabricated Si SPADs with n + -p structures and we show that dark counting has a simple exponential dependence on time, thus making it possible to extract a single lifetime parameter.

Improving ICs reliability with high speed thermal mapping

The power elements are the weak parts of integrated circuits (ICs), in fact, through these elements the power is usually dissipated as heat. This provides two effects: non-uniform generation of the heat across the die and temperature gradients. Understanding this phenomena is very important for choosing the right location of sensitive components, like thermal sensors, in order to improve reliability. Furthermore, an accurate thermal modeling for reliability evaluations can be obtained and validated if the temperature distribution on the chip is experimentally measured, reconstructing the thermal maps. Here, we propose a suitable instrument to perform a direct measure of thermal distributions. The instrument has to be able to recognize small partitions of the chip and to store fast thermal events in the range below μs. With its application, a great improvement can be obtained for ICs reliability.

Towards a nanofabricated vacuum cold-emitting triode

A technique to fabricate a vacuum cold-cathode nanoelectronic diode with a remarkably low 2-V turn-on voltage was recently presented. A three-terminal device based on the same technology is here designed and fabricated, to implement a vacuum nano-triode. The attempt was partially successful as the excessively large gate radius does not allow effective current control. Nonetheless, the obtained experimental results still disclose fundamental behaviors improving both the art and knowledge in the field. Specifically, it is found that: 1) thermionic field emission is ascertained both from a metal tip and from a silicon tip with a nearly 2-V turn-on voltage; 2) the gate current is negligible and the cathode current is efficiently collected by the anode, 3) emission is quite insensitive to temperature and the device can work also at high temperatures, observed up to 300 °C in a reliable manner. Finally, the unexpected bidirectional conduction can open a new scenario for the implementation of triac-like vacuum nanodevices.

Reliability model application for power devices using mechanical strain real time mapping

The reliability characterization is a milestone for the design of semiconductor power devices operating in those applications where a high robustness is a critical point, as in the case of the automotive field. In order to realize a reliability model that can describe the degradation of power devices, due to a cyclic thermo-mechanical stress, the Coffin-Manson equation is widely applied. Generally speaking the Coffin-Manson relationship shows a correlation between the fatigue life and the plastic strain but this equation is often customized in order to correlate the fatigue life with the temperature variations, being these simpler to measure. In this paper a methodology based on a direct measurement of the mechanical strain applied on operating devices will be shown. Furthermore, the application of the results for the reliability evaluation without taking into account the temperature variations will be described. This target has been accomplished with a suitable scanning instrument based on the laser interferometry able to perform very fast acquisitions and to reconstruct nanometric mechanical displacements.

2-V turn-on voltage field-emitting vacuum nanoelectronic device

This paper describes a cold-cathode nanoelectronic device that is compact, self-aligned to the vacuum cavity and cost-effective, as manufactured through standard silicon fabrication integrated circuit (IC) processes. Measurements on a first prototyped array of 5×4 diode-connected parallel devices with silicon area of 5um×4um, confirm Fowler-Nordheim emission with turn-on voltage as low as 2 V, while providing a total emission current of 25 μA at a gate-cathode bias of 20 V.

Thermal stress and mechanical strain real time mapping in Intelligent Power Switches device

Thermal stress and mechanical deformations are the principal causes of power devices premature failures, especially in those critical conditions where they work under repetitive high current pulses or during overloads. Currently, a large effort has been devoted, both in experimental and computer modeling techniques, to predict the lifetime of those power devices used in automotive applications where high reliability is mandatory. Moreover, the knowledge of the thermal and mechanical stress, during the operations, could allow an effective refining of the design rules to improve devices reliability. In this paper, a novel technique to experimentally measure both thermal and mechanical fatigue on IPSs (Intelligent Power Switches) is presented.

A new high energy implantation based technology for power integrated circuit devices

In this work, a significant improvement of power integrated circuit technology has been obtained by the use of high energy implantation, thus eliminating a second epitaxial growth. The damage in implanted region has been recovered by rapid thermal annealing.