Deep reactive ion etching for lateral field emission devices

The authors describe the design, fabrication and testing of lateral field emission diodes utilizing the deep reactive ion etch (DRIE). Devices were fabricated on silicon-on-insulator (SOI) wafers of varied thickness, by etching the device silicon in the STS DRIE system in a single mask process. After subsequent oxidation sharpening and oxide removal, diodes were tested on a probing station under vacuum. A typical diode exhibited very high currents on the order of ~100 μA at 60 V, and turn-on voltage between 35 V and 40 V. The high electron current is emitted in such a diode by multiple sharp tips vertically spaced by 450 nm along the etched sidewall due to the pulsed nature of the DRIE process     

Ultralow-voltage boron-doped diamond field emitter vacuum diode

A boron-doped diamond field emitter diode with ultralow turn-on voltage and high emission current is reported. The diamond field emitter diode structure with a built-in cap was fabricated using molds and electrostatic bonding techniques. The emission current versus anode voltage of the capped diamond emitter diode with boron doping, sp² content, and vacuum thermal electric (VTE) treatment shows a very low turn-on voltage of 2 V. A high emission current of 1 μA at an anode voltage of less than 10 V can be obtained from a single diamond tip. The turn-on voltage is significantly lower than comparable silicon field emitters     

A novel fabrication process of a silicon field emitter array withthermal oxide as a gate insulator

We have successfully developed a fabrication process of a silicon field emitter array with a gate insulator formed by Si₃N₄ sidewall formation and subsequent thermal oxidation. This process overcomes some problems in the conventional fabrication, such as high etch rate, low breakdown field, and gate hole expansion arising from evaporation of gate oxide. Therefore, we could improve process stability and emission performance, and also reduce gate leakage current. The optimum process conditions were determined by process simulations using SUPREM-4. The turn-on voltage of the fabricated field emitters was approximately 38 V. An anode current of 0.1 μA (1 μA) per tip was measured for a 625-tip array at the gate bias of 80 V (100 V), and the gate current was less than 0.3% of the anode current at those emission levels     

A novel structure of silicon field emission cathode with sputteredTiW for gate electrode and TEOS oxide for gate dielectric

A novel silicon field emission cathode structure with a narrow spacing between tip and gate electrode is proposed, based on the filling characteristics of the sputtered Ti_0.1W_0.9 beneath the disc-shaped tip-mask oxide. Without advanced lithography technologies, the hole diameter of the gate is reduced to a sub-half-micrometer of ~0.4 μm from an initial tip-mask size of ~1.2 μm, and the gate electrode easily approaches the cathode, leading to a low-voltage operation. A uniform and stable field emission cathode is obtained using well-established VLSI process technologies. The current-voltage (I-V) characteristics of the cathodes show low turn-on voltages of ~30 V     

Structure and electrical characteristics of silicon field emissionmicroelectronic devices

Field emission current was measured from arrays of wet chemically etched silicon cold-cathode diodes. Two types of cathode tips were measured both as-etched and after sharpening by low-temperature oxidation. The field enhancement increase resulting from tip sharpening is less than expected from simulation. The currents measured follow a Fowler-Nordheim characteristic and are temperature insensitive from 130 to 360 K. Turn-on voltage is near 4 V, a value much less than measured from most other field emission sources. With a 920-nm anode-cathode spacing, a minimum 0.2-μA current per cathode was found. Telegraph noise of about 1% at 20 V was observed. These sharpened silicon tips are a viable cold cathode for vacuum microelectronics and other electron device applications     

High current density Si field emission devices with plasmapassivation and HfC coating

A novel self-aligned process was developed to fabricate gated Si field emission devices. At a gate voltage of 100 V, the emission current from an array of 100 tips increased from 283 to 460 μA and the turn-on voltage decreased from 31 to 21 V after H₂ plasma passivation using an inductively coupled plasma (ICP) source for 2 min. The improvements correspond to a 1.28-eV reduction in the effective work function of the emitters and the instability of the emission current decreased from ±1,25 to ±0.25% after H₂ plasma passivation. Emitter tips were also coated with Mo silicide and HfC. The emission current increased from 230 μA for uncoated emitters to 268 μA for emitters coated with Mo silicide and 389 μA for emitters coated with HfC. The turn-on voltage decreased from 50 to 41 and 25 V while the breakdown voltage increased from 126 to 129 and 143 V when Mo silicide and HfC were used for coating, respectively, which correspond to reductions of 0.95 and 2.23 eV, respectively, in the effective work function of the emitters. Single emitter tips have similar emission characteristics as high-density field emitter arrays, indicating excellent emission uniformity from the arrays     

Silicide application on gated single-crystal, polycrystalline andamorphous silicon FEAs. I. Mo silicide

In order to improve both the level and the stability of electron field emission, the tip surface of silicon field emitters have been coated with a molybdenum layer of thickness 25 nm through the gate opening and annealed rapidly at 1000°C in inert gas ambient. The gate voltages of single-crystal silicon (c-Si), polycrystalline silicon (poly-Si) and amorphous silicon (a-Si) field emitter arrays (FEAs) required to obtain anode current of 10 nA per tip are 90 V, 69 V, and 84 V, respectively. In the case of the silicide emitters based on c-Si, poly-Si and a-Si, these gate voltages are 76 V, 63 V, and 69 V, respectively. Compared with c-Si, poly Si and a-Si field emitters, the application of Mo silicide on the same silicon field emitters exhibited 9.6 times, 2.1 times, and 4.2 times higher maximum emission current, and 6.1 times, 3.7 times, and 3.1 times lower current fluctuation, respectively. Moreover, the emission currents of the silicide FEAs depending on vacuum level are almost same in the range of 10^-9~10^-6 torr. This result shows that silicide is robust in terms of anode current degradation due to the absorption of air molecules     

A novel in situ vacuum encapsulated lateral field emitter triode

We have designed and fabricated a novel lateral field emitter triode, which is in situ vacuum encapsulated so that any troublesome additional vacuum sealing process is not required. The device exhibits low turn-on voltage of 7 V, stable current density of 2 μA per tip, and high transconductance of 1.7 μS per 100 tips field emitter array at V_AC=22 V. An in situ vacuum encapsulation employing recessed cavities by isotropic RIE (reactive ion etch) method and an electron beam evaporated molybdenum vacuum seal are implemented to fabricate the new field emitter triode. The superb field emitter characteristics are probably due to sub-micron dimension device structure and the pencil type lateral cathode tip employing upper and lower LOCOS oxidation     

Silicon compatible organic light emitting diode

As an effort toward a goal of monolithic optoelectronics for silicon (Si) chip-to-chip connections, we have fabricated organic light emitting diodes (LED's) using either heavily N-doped silicon (Si) as a cathode or P-doped Si as an anode. A thin silicon dioxide (SiO₂ ) layer, thermally grown on Si before deposition of a polymer or a molecular organic layer, enhances the electron injection into the semiconducting emissive layer. Without the thin oxide layer, no light was observed from LED's made from either (2-methoxy, 5-(2'-ethyl-hexoxy)-1, 4-phenylene vinylene) (MEH-PPV) or 8-hydroxyquinoline aluminum (Alq). With the SiO₂ layer,the internal quantum efficiencies as high as 0.02% and 0.5% have been observed for MEH-PPV and Alq, respectively, and the turn-on voltages were as low as 2.5 V and 8 V, again for MEH-PPV and Alq, respectively. From the LED response time measurement, we identified RC constant and the recombination time of transport-related traps as the speed limiting factors     

Arrayed silicon avalanche cathodes

Silicon avalanche cathodes (SACs) consisting of a heavily doped shallow (less than 300 A) p-n junctions were fabricated, characterized, and used as electron sources in Si-based microvacuum diodes. The emission current was investigated as a function of diode reverse-biased voltage and external field. The field was provided by an anode placed approximately 1 mm above the cathode to simulate the field which would be obtained with a built-on-chip anode. Eighteen different shapes and sizes of SACs were tested. An emission current of 0.24 μA and an emission efficiency (emission current/total diode current) of 2.1×10^-5 were observed from the single bare Si p-n junction cold cathode     

A new lateral field emission device using chemical-mechanicalpolishing

A polysilicon lateral field emission device using chemical-mechanical polishing (CMP) is proposed and experimental results on the first prototype are reported. In this method, dry oxidation process determines the interelectrode gap. Thus, it is relatively easy to form electrode gaps with dimensions less than 1 μm. Also, the process allows for good uniformity and reproducibility in controlling the interelectrode gap. The turn-on voltage of the fabricated device with interelectrode gap of 3500 Å is as low as 5.4 V and the emission current is as high as 9 μA at 9.3 V. From the Fowler-Nordheim (FN) equation, field emitting area (α) and field enhancement factor (β) are estimated to explain the low turn-on voltage and the high emission current. The emission current fluctuation is about ±4% for 25 min     

Demonstration of low voltage field emission

The authors describe field emission from a thin-film field emitter array. The process used to fabricate the field emitters is based on the mold technique described by H.F. Gray and R.F. Greene (US patent 4,307,507). Each emitter chip consists of a 10×10 square array of field emitter tips and associated lead bonding pads. There is a 10-μm spacing between emitter tips. The bare chips were packaged by mounting to an alumina substrate, four to eight chips per substrate. The chips were tested in a demountable vacuum system equipped with a movable anode. The testing apparatus makes it possible to accurately measure currents as low as 100 nA at low duty. Fowler-Nordhein-like current-voltage characteristics were measured for most of the chips tested, indicating field emission. Substantial emission currents were observed at less than 20 V. The emitted current was collected almost entirely at the anode: the measured gate current was 1 to 5% of the emitted current     

Enhancement of electron emission efficiency and stability ofmolybdenum-tip field emitter array by diamond like carbon coating

The effect of diamond like carbon (DLC) films, coated by a layer-by-layer technique using PECVD (plasma enhanced chemical vapor deposition) on the electron emission characteristics of molybdenum (Mo)-tip field emitter array (FEA) is examined. The turn-on voltage was lowered from 80 V for the Mo-tip to 65 V for the DLC-coated Mo-tip FEA while the maximum emission current was increased from 140 μA for the Mo-tip to 320 μA for the DLC-coated Mo-tip FEA composed of 900 emitters. For an anode current of 0.1 (μA/emitter) the gate voltage for the DLC-coated Mo-tip FEA and Mo-tip FEA was about 87 and 107 V, respectively. It was also confirmed that the emission current of a DLC-coated Mo-tip FEA was more stable than that of a Mo-tip FEA     

An empirical study of dynamic properties of an individual carbon nanotube electron source system

In this paper we present an empirical study of some dynamic properties of an individual carbon nanotube (CNT) field emission electron source system. We propose a circuit model that represents the CNT cathode to anode diode as a capacitor in parallel with a voltage-controlled variable resistor. The transient response of the CNT electron source system to the falling edge of a voltage step input was evaluated. For input voltages below the threshold voltage for field emission, the nanotube loop is effectively open and the circuit response is consistent with a discharging capacitor. On the other hand, for input voltages above field emission threshold, the nanotube loop conducts and now the capacitor discharges to a certain extent through the nanotube loop as well. Field emission current versus voltage data also shows that the resistance across the CNT cathode to anode diode varies as a function of applied voltage. Below turn-on voltage, the diode behaves as an open circuit (4 TΩ at the ammeter noise floor). Above turn-on voltage, resistance falls exponentially, as expected from the Fowler–Nordheim equation for cold field emission current. Experimental current–voltage data is presented for a simple emitter array consisting of two CNTs with equal lengths. Despite the similarity in their lengths the turn-on voltages of the nanotubes varied significantly, viz. 26 V versus 109 V. This large difference in the turn-on voltages can be attributed to tip imperfections. For advanced array applications such as high-throughput parallel e-beam lithography, in which precise dose control is necessary, the diode circuit model will be useful for controlling individually addressed nanotubes to account for dissimilar field emission properties. The model may also be applied to optimize the design of a SEM incorporating a single CNT electron source.     

Low turn-on voltage field emission triodes with selective growth ofcarbon nanotubes

A low turn-on voltage, field emission triode array has been fabricated using the selective deposition of carbon nanotubes (CNTs) in a microwave plasma chemical vapor deposition (MPCVD) system. The field emission triodes exhibited a low turn-on voltage of 13 V and a large emission current of 23 μA with the gate voltage at 60 V. Short-term stress reveals a 10% current fluctuation within 1800 sec. The excellent electric properties suggest that the array shows potential for application in field emission displays and vacuum microelectronics     

Improvement of electron emission efficiency and stability bysurface application of molybdenum silicide onto gated poly-Si fieldemitters

As an approach to improve electron field emission and its stability, molybdenum (Mo) silicide formation on n⁺ polycrystalline silicon (poly-Si) emitters has been investigated. Mo silicide was produced by direct metallurgical reaction, namely, deposition of Mo and subsequent rapid thermal annealing. The surface morphologies and emission properties of Mo-silicided poly-Si (Mo-polycide) emitters have been examined and compared with those of poly-Si emitters. While anode current of 0.1 μA per tip could be obtained at the gate voltage of 82 V from poly-Si emitters, the same current level was measured at 72 V from Mo-polycide emitters. In addition, the application of Mo silicide onto poly-Si emitters reduced the emission current fluctuation considerably. These results show that the polycide emitters can have potential applications in vacuum microelectronics to obtain superior electron emission efficiency and stability     

In-situ vacuum-sealed lateral FEAs with low turn-on voltage andhigh transconductance

We have fabricated a new lateral field emitter array, in-situ vacuum-sealed, which exhibits a low turn on voltage and a high transconductance value without any additional vacuum sealing process. The vacuum-sealed lateral FEA (VLFEA) is encapsulated during the fabrication process, so that field emission characteristics can be measured without any additional vacuum environments. Experimental current-voltage (I-V) characteristics show that the anode current is field emission current obeying the linearity of the Fowler-Nordheim (F-N) plot. The experimental turn-on voltage of about 9 V is in good agreement with the extracted one from the F-N plot. In order to verify the integrity of the vacuum sealed micro-cavity, we have measured the anode current of the VLFEA both in a high vacuum chamber and in an atmospheric environment and found that the structure is well sealed. The anode currents as a function of gate voltage of the Mo-sealed VLFEA are analyzed and transconductance is extracted. The experimental results show that the VLFEA has superior field emission characteristics, such as low turn-on voltage and high transconductance, and does not require any additional troublesome vacuum sealing     

Integration and characterization of amorphous silicon thin-filmtransistor and Mo-tips for active-matrix cathodes

We have designed and monolithically integrated amorphous silicon thin-film transistor (a-Si TFT) with Mo-tip field emitter arrays (FEAs) on glass substrate for active-matrix cathodes (AMCs) in field-emission display (FED) application. In our AMCs, a light shield layer of metal was introduced to reduce the photo leakage and back channel currents of a-Si TFT. The light shield was designed to have the role of focusing grid to focus emitted electron beams from the AMC on the corresponding anode pixel by forming it around the Mo-tip FEAs as well as above the a-Si TFT. The thin film depositions in a-Si TFTs were performed at a high temperature of above 360°C to guarantee the postvacuum packaging process of cathode and anode plates in FED. Also, a novel wet etching process was developed for n⁺-doped-a-Si etching with high etch selectivity to intrinsic a-Si and good etch controllability and was used in the fabrication of inverted stagger TFT with a very thin active layer. The developed a-Si TFTs had good enough performance to be used as control devices for AMCs with Mo-tip emitters. The fabricated AMCs exhibited very effective aging process for field emitters     

全丝印后栅CNT-FED仿真及器件研究

模拟并制作了一种基于丝网印刷技术的后栅结构碳纳米管场发射显示器。采用有限元分析软件ANSYS对器件进行了电场模拟,优化了阴极宽度、阴极厚度、阴极间隙、介质层厚度等结构参数。取最优参数制作了像素为30×30,发光面积为54mm×54mm的单色显示屏。在阳压为1500V、栅压为300V时,器件发射电流密度达到5μA/cm2。该器件制作成本低,稳定性和均匀性良好,可矩阵寻址实现字符显示。     

应用于LCD的平栅型碳纳米管场致发射显示器背光源的研制

采用磁控溅射、光刻和湿法刻蚀技术制备平栅型场发射阴极阵列,利用电泳将碳纳米管(CNT)发射源沉积在阴极表面,将阴极板和阳极板封接后制成51cm单色平栅型CNT场致发射显示器(CNT-FED),作为背光源模板应用于49 cm液晶显示器(LCD)器件中.场发射测试表明,器件在阳极电压3 500V、栅极电压290 V时,阳极...