development of nanocrystalline diamond

(c) Energy band diagram under bias..24 Figure 2.5 Different shapes of field emitters: (a) rounded whisker; (b) pointed pyramid;. Linear F–N diagram..134 Figure 6.15 (a) Field emission (I-E) characteristics of the considered lateral nanodiamond devices, showing the current enhancement obtained by increasing the emitter area; and (b) semi-log plot of field emission characteristics showing the electric field threshold of the three side emitters ..137.

INTRODUCTION

eV N (sub) (n)

The comparison shows that the emission characteristic is strongly dependent on the work function of the cathode. 1/E are characterized with a negative linear slope, which confirms the field emission type behavior of the current through the diamond diode device. The morphological change in the diamond film brings with it a great increase in the usability of the material.

An understanding of the physics of diamond field emission is essential to the development of an efficient diamond field emitter.

Figure 1.1 The Spindt microfabricated Molybdenum field emitter array structures [14].

Quantitatively, the RMS roughness of the nanodiamond film was found to be 8–20 nm, while that of the microdiamond film was ~115 nm. Characterization of the composition of nanocrystalline diamond: Figures 5.7 and 5.8 show the results of the Raman spectroscopic analysis performed on the nanodiamond films. Direct measurement of the electrical conductivity at room temperature (RT) showed that the nanodiamond film grew by CH4/H2/N2.

In contrast, the electrical resistance of the CH4/H2 plasma-grown nanodiamond film was found to be ~25 MΩ. Quantitatively, the nitrogen concentration was found to be cm−3 in the near-surface region (~50 Å) of the nanodiamond film. The ultra-sharp peak of the nanodiamond tip with a radius of curvature of 5 nm and a height of 1 µm is shown in Figure 5.11 (b), indicating that the 5 nm grain size of the CH4/H2/N2 nanodiamond film was incorporated into the shape transfer technique.

Due to the slightly larger particle size of the film, it can be seen that the radius of curvature (~25 nm) and peak height (~500 nm) of the peak are not as well defined as those in nanodiamond CH4/H2/ N2 tip. The field emission characteristics of nanodiamond microtip array cathodes are reported in the next chapter. With this aluminum serving as a mask, micropatterning of the nanodiamond film is performed by RIE in oxygen plasma using an ICP-RIE system to determine the electrode structures on the diamond.

Figure 5.2 SEM micrographs portraying the decrease in diamond grain size due to the reduction in CH 4 flow rate at a constant microwave power of 1000 W and reactant pressure of 28 Torr:

Nanodiamond cathode

Nanodiamond anode

Figure 5.19 (a) and (b) show the construction of nanodiamond lateral chamber array diodes comprising 650 and 9000 emitter fingers, respectively. These high-power configurations of the lateral device include symmetrically arranged arrays of comb-shaped structures, each comb consisting of 65 nanodiamond finger-like emitters as shown in Figure 5.20. The Ti/Au layer was then annealed at 300 °C in vacuum to improve the adhesion strength of the metal contact to the diamond.

Since nitrogen-incorporated nanocrystalline diamond is an excellent electron emitter, a non-diamond material is preferred for the anode component of the diode side device. The structure of the developed lateral field emission diode is shown in the main SEM micrograph of Figure 5.27, illustrating that the diamond cathode and nickel anode are precisely aligned to establish an interelectrode gap of 4 µm. The chip-type architecture of the side device is suitable for hassle-free packaging with device assembly.

Field emission characterization results for the side device operating in the package setup are presented in Chapter VI. The emission current from the nanodiamond emitters was measured as a function of the applied voltage in both forward and reverse bias directions to confirm the absence of any leakage current in the observed field emission. The emission current from the nanodiamond fingered emitter cathode was measured as a function of the applied anode voltage.

Figure 5.18 (a) A completely integrated nanodiamond lateral field emission triode, with 2 µm gate-cathode and 20 µm anode-cathode spacings; (b) A lateral triode structure, showing a high aspect-ratio nanodiamond finger-emitter in close proximity with the

Vac: 10 -7 Torr

The observed electric turn-on field of the nanodiamond lateral emitter is significantly lower than that of a comparable silicon lateral field emitter using a sharp tip, i.e. >. All these factors ensure that the emission characteristics of the lateral diode are contributed exclusively by nanodiamond. The field emission I-E behavior and the corresponding F-N plot were obtained from each of the emitters and compared.

Characterization results: The field emission characteristics of the three different emitters are presented in Figure 6.8. The effect of the geometry of the high aspect ratio fingers and the edge emitters on field emission of the nanodiamond film was studied. The observed field emission enhancement of the micropatterned nanodiamond emitters can be explained by an increase in the geometric enhancement factor.

It was also deduced that the βg of the edge emitter was ~6 times that of the deposited nanodiamond film. The magnitude of the electric field defined by each contour was found to scale linearly with the anode voltage. The high current field emission behavior of the nanodiamond 6-finger lateral diode is shown in Figure 6.14 with the current density estimate in an I-J-V plot.

Figure 6.5 Low-voltage field emission characteristics of the nanodiamond 6-finger lateral diode with 3 µm anode–cathode gap; I–V plot indicates turn-on voltage of 5.9 V; inset: linear F–N plot

Voltage (V)

Alternatively, considering the cross-sectional area of the electron collector in the side structure of the device, the anode current density is found to be as large as 1.5x103 A/cm2. The ~1 mA emission current behavior obtained from the 6-finger nanodiamond side diode initiated further work on side emitters for high power applications. Versatile side diode designs equipped with uniformly spaced high aspect ratio emitters in a large area array configuration while maintaining a small footprint were created, fabricated and characterized for high current and equal anode-cathode.

Current Density (A/cm2)

Field emission sensitivity has been previously studied, but achieving a linear scaling relationship of the emission behavior with the separation distance between the electrodes is a challenge. Pressure/Vibration/Acceleration to deflect the cantilever side beam. h) Emission current stability characteristics of the nanodiamond lateral device. The emission behavior of the nanodiamond side emitter was found to be repeatable and stable over time.

An idea of the emission stability of the side device can be obtained from Figure 6.26, with a current fluctuation of ~ 2 % over a time period of 80 minutes under a vacuum of 10-6 Torr for a given applied electric field. These charge carriers can cause transient artifacts in device operation (soft errors), and in some cases, permanent damage (hard errors). Temperature tolerance characteristics: To evaluate the temperature insensitivity of the nanodiamond lateral VFEM, some of the nanodiamond lateral diodes were subjected to temperature testing in a vacuum chamber maintained at 10-7 Torr.

No leakage current via the SiO2 layer was observed in the emission current and the electrical behavior of the diode was not affected by the varying temperatures. Note the total independence of the device's forward current on temperature, indicating the operational temperature immunity of the nanodiamond lateral vacuum device. The corresponding linear Fowler-Nordheim (F-N) plots, as seen in the inset of the two graphs, confirm that the observed current is attributable to field emission.

Figure 6.24 Virtually unchanged field emission (I-E) characteristics obtained from the lateral vacuum devices; inset is the semi-logarithmic plot showing the turn-on electric field of ~ 2 V/µm for the three diodes

Electric Field (V/µ m)Current (µA)

The negative linear slopes of the FN plots (insets of Figures 6.29 and 6.30) indicate that the emission data are consistent with the field emission behavior. Furthermore, the linear slopes remain unchanged as a function of radiation dosage, confirming that the irradiation did not cause any change in the work function or field enhancement factor of the emitting surface. Figures 6.31 (a) and (b) show the diode emission current as a function of irradiance, using an average dose rate of 31.5 krad(SiO2)/min, operating at different applied doses.

Since the nanodiamond lateral VFEM is fabricated on a SOI substrate, C-V measurements of the SOI structure were performed to investigate the effect of charge trapping in the SiO2 layer and its subsequent effect on VFEM performance. It can be observed that the absolute value of the capacitance has changed, indicating that significant hole trapping has occurred due to radiation in the buried oxide and the SiO2-Si interface. Post-irradiation C-V measurements indicate rapidly trapped mobile charges in the SOI substrate. However, this perturbation does not affect the performance of the lateral VFEM nanodiamond (Figs. operating on a SOI substrate.

Thus, the material system and device construction of the nanodiamond lateral field emission vacuum device is important for ultra-hardened electronics and can be useful for high-temperature and rad-hard scientific, defense, and commercial communities. j) Rectification behavior of nanodiamond lateral field emission diode. As mentioned in point (b) of this section, by comparing the field emission characteristics of different nanodiamond side emitter geometries, the superior geometric field enhancement of the high aspect ratio finger-like emitter structure has been experimentally established. on the edge structure. The shallow slope is indicative of a high β factor of the side device nanodiamond emitter.

Figure 6.30 Field emission behavior of the nanodiamond lateral diode (Pre-Rad, 15 Mrad); inset:

Electric Field (V/µm)Current (µA)

The different three-terminal lateral configurations were tested to investigate the triode characteristics of the device. It has been identified that the position of the electrodes in the device design plays a significant role in determining its properties. The functionality of the lateral emitter device as a triode or a transistor can be manipulated by lithographically changing the design of the three-terminal structure.

The operation of nanodiamond lateral field emission device in triode and transistor modes is described in this section. The low applied electric fields required to initiate and modulate the electron emission between the electrodes are attributed to the geometry and material composition of the nanodiamond lateral emitter. This transconductance parameter was determined to be ~0.3 µS at Va = 65 V, one of the highest reported for lateral devices involving a single emitter, especially with the cathode-gate separation in microns.

The demonstration of a lateral field emission transistor on the microelectronic scale is essential for the development of the vacuum IC. The device was operated in a gate-induced emission mode, where the anode potential (collector potential) contributed an insignificant component to the electric field at the emitter finger tip. Overall, the field emission data demonstrated the basic transistor characteristics of the lateral nanodiamond device with clear boundary, linear, and saturation regions in a triode configuration.

Figure 6.35 (a) Structure of the integrated nanodiamond lateral field emitter vacuum microtriode with 3 µm gate-cathode and 12 µm anode-cathode spacings; (b) Triode characteristics of the 1-finger lateral device; inset: F-N plot of one of the I-V curves

Anode Voltage, V a (V)Anode Current, Ia (µA)

The negative linear slope of FN further indicates that the unit current is due to the field emission tunneling mechanism. The electrical insulation integrity of the cathode-gate-anode in the monolithic transistor device was confirmed from the observation of zero leakage. The transistor parameters of the triode amplifier were determined graphically from the dc characteristic curves.

Note that the amplification factor can be expressed as the product of the anode resistance and the transconductance, μ=ra.gm. The anode resistance, ra of the transistor is calculated to be ~10 GΩ, useful in amplification applications that require high output impedance. Simple control of the lithography process over the side gate-cathode gap will directly adjust the threshold voltage of the vacuum transistor.

Similar to the results achieved with the lateral diode, no effect of radiation was observed on the field emission I-V characteristics of the monolithic diamond vacuum transistor. In the future, a lateral emitter array structure can be developed to improve the performance of the vacuum transistor. The emission appeared to comply with the F-N behavior; the F-N plots of the lateral nanodiamond diodes are straight lines with a negative slope.