Chengye Dong

Demonstration of field emission driven microscale gas breakdown for pulsed voltages using in-situ optical imaging

While multiple studies have explored the mechanism for DC and AC microscale gas breakdown, few have assessed the mechanism for pulsed voltage gas breakdown at the microscale. This study experimentally and analytically investigates gas breakdown for gap widths from 1 μm to 25 μm. Using an electrical-optical measurement system with a spatial resolution of 1 μm and a temporal resolution of 2 ns, we measure the breakdown voltages and determine breakdown morphology as a function of the gap width. An empirical fit shows that the breakdown voltage varies linearly with the gap distance at smaller gaps, agreeing with an analytical theory for DC microscale gas breakdown coupling field emission and Townsend avalanche that shows that the slope is a function of field emission properties. Furthermore, the curved breakdown paths captured between 5 μm and 10 μm demonstrate a similar effective length (∼11.7 μm) independent of the gap width, which is consistent with a “plateau” in breakdown voltage. This indicates that Townsend avalanche alone is insufficient to drive breakdown for these gaps and that ion enhanced field emission must contribute, in agreement with theory. The overall agreement of measured breakdown voltage with theoretical predictions from 1 μm to 25 μm indicates the applicability of DC microscale gas breakdown theory to pulsed breakdown, demonstrating that pulsed voltages induce a similar transition from Townsend avalanche to field emission as DC and AC voltages at the microscale.While multiple studies have explored the mechanism for DC and AC microscale gas breakdown, few have assessed the mechanism for pulsed voltage gas breakdown at the microscale. This study experimentally and analytically investigates gas breakdown for gap widths from 1 μm to 25 μm. Using an electrical-optical measurement system with a spatial resolution of 1 μm and a temporal resolution of 2 ns, we measure the breakdown voltages and determine breakdown morphology as a function of the gap width. An empirical fit shows that the breakdown voltage varies linearly with the gap distance at smaller gaps, agreeing with an analytical theory for DC microscale gas breakdown coupling field emission and Townsend avalanche that shows that the slope is a function of field emission properties. Furthermore, the curved breakdown paths captured between 5 μm and 10 μm demonstrate a similar effective length (∼11.7 μm) independent of the gap width, which is consistent with a “plateau” in breakdown voltage. This indicates that Tow...

Two-dimensional mapping of the electric field distribution inside vacuum microgaps observed in a scanning electron microscope

In this paper, we present an in-situ measurement method to directly observe the distribution of the local electric field between vacuum microgaps. The measurement was performed in-situ inside a high resolution scanning electron microscope (SEM), and the nature of the local electric field was characterized through secondary electron contrast images with the aid of Rutherford scattering theory. Based on the regular fringes in these contrast images, the distribution of the local electric field could be extracted from the contour lines of the fringes while the magnitude of the local electric field could be evaluated qualitatively by the gradient of the contour lines. The finite element method (FEM) simulation and the three-electrodes imaging experiment were also conducted, and the obtained two-dimensional electric field distribution agreed well with the FEM simulation, suggesting that the in-situ visualization technique could be useful for determining the local field enhancement behavior for various geometrical configurations and microscale structures. A physical mechanism for the local electric field mapping is suggested. This study demonstrates the potential of SEM imaging for obtaining information about the local electric field within microelectronic structures and devices.

The design of automatic test system used for PDIV measurement of inverter-fed motor

In order to study the partial discharge (PD) characteristics and evaluate the insulation conditions of the inverter-fed motor under sinusoidal voltage automatically, a set of automatic test system is designed based on high frequency current transformer (HFCT) detection technologies. In the system six high-voltage relays are connected with three-phase windings and the grounded enclosure of the motor. By controlling the six different high-voltage relays (on or off) through the FPGA and with the help of high speed data processing function of DSP, all the partial discharge inception voltage (PDIV) of the phase-to-phase and phase-to-ground insulations can be measured automatically. To verify the test performance of the system, PDIV of twisted pair with polyimide film was measured firstly, and then the phase-to-phase and phase-to-ground insulations of an inverter-fed motor were tested. The results shows: The PDIV of the twisted pairs is about 1.85 kV. The phase-to-phase PDIV of the tested motor is about 3.25 kV, while the PDIV of each phases to ground is obviously higher, reaching more than 5 kV. Compared with traditional test methods, this system can not only measure the PDIV of insulations in the motor automatically, but also greatly reduce the amount of labor and improve test efficiency and accuracy. Therefore, it is especially suitable for testing and evaluating the insulation conditions of large number of motors so as to prevent premature insulation failures and elongate the durability of the motors.

Influence of crystal morphology on breakdown characteristics in vacuum between nano scale gaps

With the rapid miniaturization of electronic components, it is urgent to study the mechanism of breakdown in micro and nano scale. In this paper, the influence of crystalline morphology on breakdown characteristics between nano scale gaps in vacuum was studied by using Kleindiek nano manipulator and Keithley 6517B electrometer. Monocrystalline and polycrystalline molybdenum needles (apex curvature radii less than 50nm) were used as cathodes respectively, while tungsten spheres (curvature radii about 15μm) were used as anodes. It is found that in the fixed gap widths (100nm), the average value of breakdown thresholds of monocrystalline cathodes is lower than that of polycrystalline cathodes. The results of experiments were analyzed from 3 different aspects: pre-breakdown process, breakdown thresholds and damage of electrodes after breakdown. This study shows that crystalline morphology has an important influence on breakdown charcteristics in nano scale, which would be helpful to design nano scale electronic components in the future.

Investigation on breakdown characteristics between microscale gaps under nanosecond pulse

As the microelectronic devices have been widely used in modern society, their safety and reliability while working in high field strength are taken into account and it is significant to study the breakdown mechanism between microscale gaps under nanosecond pulse. Based on the electrical measurement system for microscale breakdown, a dedicated optical acquisition system has been established to record the lighting images of the whole discharge process. This paper mainly focuses on the study of breakdown intrinsic laws between microscale gaps and the investigation of optical characteristics when discharges occur. Breakdown thresholds of different gap widths from 1μm to 100μm are measured and typical breakdown waveforms are recorded. Through optical acquisition system, optical images of different periods are captured. Different mechanisms affect in different gaps and pre-breakdown stage, breakdown developing stage and self-sustained stage compose the whole discharge period. Optical images show a complete developing process of arc. The series of results would make a further guidance for breakdown mechanism between micrometer gaps.

Effect of electrode geometry on the vacuum breakdown behaviors at nanoscale

The micro/nano devices have been widely used for the past decades. However, as one of the major factors to restrict the performance of the devices, the insulation failure mechanism at nanoscale is still unclear. Basically, the insulation performance in vacuum is related to the electrode geometry, electrode materials, gap size and applied voltage, etc. To better understand the mechanism of vacuum breakdown at nanoscale, the present work focuses on the effect of electrode geometry on nanoscale breakdown in vacuum. The effect of the electrode geometry would be investigated experimentally and the mechanism would also be discussed in the paper.

Effect of electrode materials on the vacuum breakdown behaviors at nanoscale

As electronic and electro-mechanical devices with high integration density have been universally employed in many fields of science and engineering, the insulation failure under high electric field become one of the major factors limiting the performance of micro/nano systems. Herein, the pre-breakdown and breakdown characteristics of tungsten (W) and molybdenum (Mo) needle electrodes across a 100-nm vacuum gap were investigated. In the pre-breakdown process, the current linearly increased with the applied voltage. The field emission played a dominated role in the vicinity of the breakdown threshold. Furthermore, the breakdown threshold of W needle electrode was 19.5% higher than that of Mo needle electrode owing to a similar work function and a higher melting point of W needle electrode compared with Mo needle electrode. The study would be beneficial to the choice of materials and the reliability analysis of micro/nano devices.

Physical damage effect of microelectrodes under nanosecond pulse induced breakdown

Electrical breakdown due to overvoltage may result in a series of performance degradation and physical damage to microelectronic devices. In this paper, we present the physical damage effect of nanogaps in microelectronic devices and explore the relationship between the morphology change and injected energy during breakdown process. The nanoscale discharge characteristics experimental system based on a focused ion beam, a nanometer manipulator and a DC power supply generator was established, which could be used to simulate the typical nanosecond pulse impact event while electrostatic charge accumulates between the nanogaps. Different types of voltage stresses were applied to tungsten microelectrodes so as to understand the relationship between physical morphology change and injected energy. The morphology change process was obtained and the mechanism for the multi-physical coupling induced physical damage was then put forward.

Prebreakdown investigations of vacuum discharge between nano gaps

The electrical breakdown behavior between nano vacuum gaps is vital with the miniaturization of electronic and electromechanical devices, which is mainly determined by the prebreakdown process. Therefore, the prebreakdown characteristics of different electrode configurations in vacuum gap were investigated in this paper using an in-situ scanning electron microscopy (SEM) and piezoelectric displacement approach. The measurement of current between the sphere-sphere electrodes revealed two distinct stages: (a) a low leakage current of 1×10-11 A during the prebreakdown process; (b) the occurrence of a current pulse of 10-3 A and the breakdown took place at a critical voltage. In contrast, the current showed three stages for the needle-sphere electrodes: (a) a low leakage current of 1×10-11 A the same as the sphere-sphere configuration; (b) an exponential field emission current; (c) a current pulse of 10-7 A was detected and the breakdown took place. The difference of prebreakdown current implied that for the quasi uniform field gap the field emission turned on simultaneously from the whole area of the cathode surface and the threshold field was nearly equal to the dielectric strength.