[Show abstract][Hide abstract] ABSTRACT: This article reviews recent development of the vertically configured vacuum field emission integrated devices utilizing nanodiamond microtip emitters and their further implementation into circuits. The device design, fabrication and characterization of the nanodiamond vacuum field emission functional devices including transistor and triode are discussed. The realization of the basic circuit building block – differential amplifier – is also reported, indicating the feasibility of vacuum-based ICs. These developments provide a promising method for accomplishing vacuum-based microelectronics. Recent development of nanocrystalline diamond has demonstrated its superior electron field emission properties and prompted the interest in the utilization of nanodiamond for vacuum microelectronics . Apart from the advantages of conventional microcrystalline diamond , nanodiamond with n-type conductivity and deliberate inclusion of sp 2-carbon in sp 3-diamond matrix can be achieved by in situ nitrogen incorporation in chemical vapor deposition of nanodiamond films to provide enhanced electron emission characteristics . Besides, the small grain size and smooth surface morphology of nanodiamond facilitate the compatible integration with silicon microfabrication, expanding its utility for practical applications. Micropatterned nanodiamond microtip emitters with high geometric field enhancement factor have also been reported and exhibited excellent electron field emission characteristics with high and stable emission current at low electric field . The realization of efficient nanodiamond emitters has helped to establish the fundamental fabrication process for further implementation of three-terminal nanodiamond vacuum field emission (VFE) devices and integrated circuits (ICs). This paper presents the design, fabrication, material properties and electrical characterization of nitrogen-incorporated nanodiamond VFE functional devices and ICs, specifically focusing on vertically configured VFE transistors, triodes, and differential amplifiers. The three-terminal nanodiamond VFE device is comprised of an array of nanodiamond pyramidal microtip emitters, an integrated silicon side-gate and a silicon top-anode located above the emitters supported by an insulated layer. The device is fabricated by employing an IC-compatible self-aligned emitter-gate technique on silicon-on-insulator (SOI) wafer coupled with chemical vapor deposition of nanodiamond films. The active-silicon layer of the SOI is utilized as self-aligned gate of the three-terminal device. The buried-oxide (BOX)
28th International Vacuum Nanoelectronics Conference, Guangzhou, Guangdong Province, China; 07/2015
[Show abstract][Hide abstract] ABSTRACT: This article reports a vacuum field emission microtriode utilizing nanodiamond as the emitting material. The device was fabricated by IC-compatible fabrication process involving a mold transfer technique coupled with nanodiamond chemical vapor deposition. Triode behavior was characterized, showing gate-controlled emission current modulation with high current density at low bias conditions. A high current density of ~150 mA/cm 2 is achievable at low operating gate and anode voltages. It was found the nanodiamond microtriode can be used as a buffer amplifier for high frequency applications. The realization of an efficient vacuum microtriode achieves a fundamental step for further development of vacuum integrated microelectronics.
28th International Vacuum Nanoelectronics Conference, Guangzhou, Guangdong Province, China; 07/2015
[Show abstract][Hide abstract] ABSTRACT: The desorption kinetics of deuterium from polycrystalline chemical vapor deposited diamond films were characterized by monitoring the isothermal thermionic emission current behavior. The reaction was observed to follow a first-order trend as evidenced by the decay rate of the thermionic emission current over time which is in agreement with previously reported studies. However, an Arrhenius plot of the reaction rates at each tested temperature did not exhibit the typical linear behavior which appears to contradict past observations of the hydrogen (or deuterium) desorption reaction from diamond. This observed deviation from linearity, specifically at lower temperatures, has been attributed to non-classical processes. Though no known previous studies reported similar deviations, a reanalysis of the data obtained in the present study was performed to account for tunneling which appeared to add merit to this hypothesis. Additional investigations were performed by reevaluating previously reported data involving the desorption of hydrogen (as opposed to deuterium) from diamond which further indicated this reaction to be dominated by tunneling at the temperatures tested in this study (<775 °C). An activation energy of 3.19 eV and a pre-exponential constant of 2.3 × 1012 s−1 were determined for the desorption reaction of deuterium from diamond which is in agreement with previously reported studies.
[Show abstract][Hide abstract] ABSTRACT: Geo-political concerns, global warming, damage to ecosystem and biodiversity have resulted in greater focus on research and development of alternative energy sources. Energy storage became a dominant factor in economic development with the global energy consumption forecast to grow by 56% between 2010-2040 with renewable energy expected to grow at 2.5% per year . Solar and wind energy are very consistent from year to year but have significant variation over shorter time frames. Batteries and ultracapacitors have been deployed to better utilize these energy sources. However, by developing advanced ultracapacitors which provide greater energy density while retaining high power density we can revolutionize energy storage solutions for both military and civilian applications. Supercapacitors are rechargeable electrochemical energy storage devices which can provide high capacitance, suitable for high power applications . Based on the charge storage mechanism, supercapacitors can be divided into three typical classes: (i) electrochemical double layer capacitors (EDLCs), (ii) pseudocapacitors, and (iii) hybrid-supercapacitors. By developing hybrid-supercapacitors which integrate high specific surface area CNTs and thin-film of pseudocapacitive MnO 2 material, we can achieve high performance at low cost. In addition to the double layer capacitance from the high surface area, we get additional capacitance from the pseudocapacitive behavior involving rapid, reversible faradaic reactions where the oxidation state of Mn varies between +3 and +4 in conjunction with the intercalation and deintercalation of the electrolyte cation, as represented by the following equation [2,3]: MnO 2 + X + + e -↔ MnOOX (X= H, Li, Na, K).
[Show abstract][Hide abstract] ABSTRACT: A three-electrode nanodiamond vacuum field emission (VFE) device with gate modulated triode characteristics is developed by integrating nanodiamond emitter with self-aligned silicon gate and anode, employing a mold transfer technique in conjunction with chemical vapor deposition of nanodiamond. Triode behavior showing emission current modulation with high current density at low operating voltages is achieved. A systematic analysis based on modified Fowler-Nordheim theory is used to analyze gate modulated VFE characteristics, confirming the triode field emission mechanism and operating principle. The realization of an efficient VFE microtriode has achieved the fundamental step for further development of vacuum integrated microelectronics.
[Show abstract][Hide abstract] ABSTRACT: A highly selective, sensitive, and stable non-enzymatic glucose sensor based on Ni hydroxide modified nitrogen-incorporated nanodiamonds (Ni(OH)2-NND) was developed. The sensor was fabricated by e-beam evaporation of a thin Ni film on NND followed by the growth of Ni(OH)2 using an electrochemical process. It was found that the Ni film thickness greatly affects the morphology and electro-catalytic activity of the as-synthesized electrode for non-enzymatic glucose oxidation. Owing to its nanostructure characteristics, the best sensor fabricated by 150 nm Ni deposition showed two wide response ranges, namely, 0.02-1 mM and 1-9 mM, with sensitivities of 3.20 and 1.41 mA mM(-1) cm(-2), respectively, and a detection limit of 1.2 μM (S/N = 3). The sensor also showed good long-term stability as well as high selectivity in the presence of interferences such as ascorbic acid, acetaminophen, and uric acid. This finding reveals the possibility of exploiting the NND as an electrochemical biosensor platform where high performance addressable sensor arrays could be built.
The Analyst 04/2013; 138(11). DOI:10.1039/c3an36679k · 4.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Microelectrodes have several benefits over macroelectrodes by virtue of their size. Their advantages include lower capacitance and uncompensated resistance loss, enhanced temporal and spatial resolution, usability in highly resistive media, increased signal to noise ratio. An array of microelectrodes can deliver these benefits along with signal amplification. Neurotransmitters, such as dopamine, undergo rapid fluctuations in concentrations occurring at a sub-second time scale. Real-time monitoring and measurement of these concentration changes, in-vivo or in-vitro, requires the use of ultra-microelectrode arrays (UMEAs). A nitrogen incorporated nanodiamond UMEA was fabricated using silicon microfabrication technology and microwave plasma enhanced CVD process. The array of 2500 UMEs, projects above the SiO2 insulating matrix, thus providing a 3-dimensional surface. Fast scan cyclic voltammetry at 300V/s was used to examine the temporal response and sensitivity for dopamine detection. A large negative holding potential was employed to promote dopamine pre-concentration in between the voltage scans.
[Show abstract][Hide abstract] ABSTRACT: Ultra-microelectrode arrays (UMEAs) are widely used because of advantages such as low capacitance and low iR losses, which provides a high signal/noise ratio and allows use in highly resistive media. They also can be used in applications requiring high temporal and spatial resolution. Hemispherical diffusion enhances the flux density at the microelectrode surface to provide greater sensitivity than macroelectrodes. Catecholamine neurotransmitters, such as dopamine, play important roles in the mammalian central nervous system and require constant monitoring and measurement. A nitrogen incorporated nanodiamond UMEA was fabricated using silicon microfabrication technology and microwave PECVD process by using a 'top-down' approach. This process allows greater control over the UMEA dimensions and nanodiamond microstructure. The array consists of 2500 UME 'mesas' projecting above the surrounding insulating matrix of spin-on-dielectric. Cyclic voltammetry was used to characterize the UMEA for detection of dopamine.
[Show abstract][Hide abstract] ABSTRACT: This article reports a vacuum multi-finger monolithic microtriode utilizing nanodiamond as the emitting material. The structure is comprised of 140-fingerlike nanodiamond emitters with built-in nanodiamond gate and Si anode. A mixed lithography patterning approach is used to fabricate the three-terminal device structure. Triode characteristics, demonstrating gate controlled emission current modulation at low operating gate and anode voltages, are obtained. The realization of the efficient monolithic microtriode allows further development of robust vacuum integrated circuit for application in high temperature and radiation harsh environments.
[Show abstract][Hide abstract] ABSTRACT: The development of a novel vacuum differential amplifier (diff-amp) array employing vertically configured nanodiamond (ND) vacuum field emission transistors (ND-VFETs) on a single chip is presented. The diff-amp array is composed of a common ND emitter array integrated with partition gates and split anodes. An identical pair of ND-VFETs with well-matched field emission transistor characteristics was fabricated by using a dual-mask well-controlled microfabrication process, involving a mold-transfer self-aligned gate-emitter technique in conjunction with ND deposition into the micropatterned molds in the active layer of a silicon-on-insulator substrate followed by gate partitioning to form diff-amp array. The ND-VFETs show gate-controlled modulation of emission with distinct cutoff, linear, and saturation regions. Signal amplification characteristics of the ND-VFET diff-amp are presented. A large common-mode-rejection ratio (CMRR) of 54.6 dB was measured for the diff-amp. The variation of CMRR performance with transconductance was examined, and the results were found to agree with the equivalent circuit model analysis. The accomplishment of this basic circuit building block, consisting of an integrated diff-amp, demonstrates the feasibility of using vacuum integrated circuits for practical applications, including high-radiation and temperature-tolerant space electronics.
IEEE Transactions on Electron Devices 01/2013; 60(1):487-493. DOI:10.1109/TED.2012.2228485 · 2.47 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Hydrogen influences many properties of diamond films, such as invoking negative electron affinity, inducing increased electron emission from diamond thermionic emitters. However, the thermionic emission diminishes at temperatures exceeding 750 °C. In this work, we observed the isothermal thermionic emission decrease followed first-order rate kinetics. Arrhenius examination indicated an activation energy consistent with values for the H-C bond at the surface derived from other works. Results obtained in this study establish a direct link between the presence of hydrogen and the degree of thermionic emission from diamond and is information relevant to the development of higher thermal emission from diamond.
[Show abstract][Hide abstract] ABSTRACT: Reported is a novel vacuum field emission transistor (VFET) differential amplifier (diff-amp) utilising nanocrystalline diamond emitters with self-aligned gate partitions. The integrated VFET diff-amp was fabricated by a dual-mask self-aligned mould transfer method in conjunction with chemical vapour deposited nanodiamond. Identical pairs of devices with well-matched field emission transistor characteristics were obtained, realising a negligible common-mode gain, high differential-mode gain, and large common-mode rejection ratio (CMRR) of 55 dB. The emission current was validated by a modified Fowler-Nordheim equation in transistor configuration, and the CMRR was modelled by an equivalent half-circuit with the calculated result found to agree well with the experimental value.
[Show abstract][Hide abstract] ABSTRACT: Nitrogen-incorporated nanocrystalline diamond (ND) vacuum field emission transistor (VFET) with self-aligned gate is fabricated by mold transfer microfabrication technique in conjunction with chemical vapor deposition (CVD) of nanocrystalline diamond on emitter cavity patterned on silicon-on-insulator (SOI) substrate. The fabricated ND-VFET demonstrates gate-controlled emission current with good signal amplification characteristics. The dc characteristics of the ND-VFET show well-defined cutoff, linear, and saturation regions with low gate turn-on voltage, high anode current, negligible gate intercepted current, and large dc voltage gain. The ac performance of the ND-VFET is measured, and the experimental data are analyzed using a modified small signal circuit model. The experimental results obtained for the ac voltage gain are found to agree with the theoretical model. A higher ac voltage gain is attainable by using a better test setup to eliminate the associated parasitic capacitances. The paper reveals the amplifier characteristics of the ND-VFET for potential applications in vacuum microelectronics.
[Show abstract][Hide abstract] ABSTRACT: This article reports successful fabrication and characterization of vacuum microelectronic OR gate logic using nanodiamond lateral diode structures. Two identical sets of four nanodiamond lateral diodes with different numbers of emitters, viz., 125, 325, 2340 and 9360, and with equal anode–cathode spacing of ~ 3.5-μm were fabricated on silicon-on-insulator (SOI) wafers. First the fabricated lateral emitters were characterized for emission current scaling to examine the scaling effect of different structures with respect to the forward emission current. Then, two identical diodes were connected in a circuit using diode–resister logic to realize the logic OR function with a square wave as an input signal. The current scaling behavior, demonstrating 1 μA current at 18, 15, 7 and 2.2 V for 125-, 325-, 2340- and 9360-fingered emitter structures respectively, directly affects the logic OR response. These nanodiamond vacuum logic gates are promising for application in harsh environments.
Diamond and Related Materials 03/2012; 23:120–124. DOI:10.1016/j.diamond.2012.01.030 · 1.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this paper, we report an innovative nanodiamond field emitter structure consisting of an individual pyramidal tip sitting on top of a ballast resistor “pole.” The tip-on-pole nanodiamond structures are fabricated by a new mold transfer process that is comprised of reactive-ion-etching of 3.5 μm-thick thermal oxide on Si substrate, anisotropic etching of Si, tip sharpening by thermal oxidation and chemical vapor deposition of nanodiamond. The fabricated tip-on-pole nitrogen-incorporated nanodiamond emitter exhibits a low turn-on electric field of 3.5 V/um and a very high emission current density of ∼1.7 A/cm2 at an electric field of ∼7.5 V/um. Analysis of the emission current based on Fowler–Nordheim theory indicates a current regulated regime due to the pole-structured ballast resistor with the resistance value of ∼140 kΩ. Thus, the diamond pole ballast resistor has proven to provide self-limiting of emission current that improves the total current density as well as the emission current stability of the pyramidal nanodiamond emitters. Therefore, the proposed tip-on-pole nanodiamond emitters show great promise for high current and power applications.
Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures 03/2012; 30(2):2204-. DOI:10.1116/1.3684425 · 1.36 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Although hydrogen has been shown to enhance the thermionic emission properties of nitrogen-incorporated diamond cathodes, the effect diminishes when these cathodes are heated to temperatures in excess of 700 °C, possibly due to the hydrogen desorbing from the diamond. In order to further examine this behavior, this work examines the thermionic emission properties of a nitrogen-incorporated diamond film grown by chemical vapor deposition in a hydrogen-methane-nitrogen plasma. The film was tested for thermally stimulated electron emission at temperatures ranging from 500 to 900 °C in an as-grown state and after exposure to a hydrogen plasma treatment. Emission current increased, as described by the Richardson equation for thermal emission up to ∼ 700 °C. Above ∼ 800 °C the thermionic emission current was observed to diminish, an effect attributed to the loss of hydrogen from the diamond. Recovery of the hydrogen effect was explored by exposing the diamond film to a low-energy hydrogen plasma. The thermionic emission current at temperatures below ∼700 °C after this hydrogen plasma exposure was observed to increase by four orders of magnitude over the thermionic emission current observed in the initial (as-grown) test. Possible explanations for this emission current increase are discussed.
Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures 03/2012; 30(2):1202-. DOI:10.1116/1.3684982 · 1.36 Impact Factor