Kwangsik Choi

A Focused Asymmetric Metal–Insulator–Metal Tunneling Diode: Fabrication, DC Characteristics and RF Rectification Analysis

Asymmetric thin-film metal-insulator-metal (MIM) tunneling diodes have been demonstrated using the geometric field enhancement (GFE) technique in a Ni/NiO/Ni structure. The GFE technique provides several benefits: generating asymmetric tunneling currents, lowering tunneling resistance, increasing nonlinearity, enhancing the effective ac signal amplitude, and improving zero-bias rectifying performance. The GFE technique can be merged with a dissimilar electrode method and use surface plamon resonances for further performance improvement. In this paper, we disclose techniques for fully exploiting all these advantages. Detailed descriptions of process flows are provided. Performance improvements are experimentally verified by measuring the static current-voltage and dynamic (6.4 GHz) response of the developed Ni/NiO/Ni tunnel diodes.

New Process Development for Planar-Type CIC Tunneling Diodes

A planar-type conductor-insulator-conductor tunneling diode is developed using a boiling water process for surface oxidation. First, microsized bow-tie patterns are transferred on a doped polysilicon layer using e-beam lithography. After reactive ion etching, the polysilicon bow-tie pattern has a very narrow knot between two triangles. Using a buffered oxide etchant (BOE) solution, hydrogen silsesquioxane patterns and native oxide layer are etched. The knot is oxidized by a boiling water oxidation process. By repeating the BOE etch and oxidation, the bow-tie patterns are transformed into tunneling diodes with a very thin oxide barrier separating two polysilicon conductors. We show that the resulting structures follow the Simmons tunneling current-voltage relationship after boiling. Moreover, a high sensitivity of 31 V-1 is achieved at a bias voltage of 80 mV.

A radio-frequency energy harvesting scheme for use in low-power ad hoc distributed networks

While RF energy harvesting has proven to be a viable power source for low-power electronics, it is still a challenge to obtain significant amounts of energy fast and efficiently from the ambiance. Available RF power is usually very weak, resulting in a weak voltage applied to a demodulator to drive it into a region of significant nonlinearity. An RF energy harvesting system consisting of a rectenna, a dc-dc voltage converter, and a novel battery cell is proposed. The rectenna is an integration of an antenna and rectifying diodes. In addition, a switched-capacitor dc-dc voltage converter is integrated on a silicon integrated circuit with energy transfer efficiency as high as 40.5%. A new battery system that can be recharged at low voltage (<; 1.2 V) is demonstrated. In this brief, all of these elements are tested as a system to achieve RF battery recharging from a commercially available hand-held communication device. The system exhibited an overall harvesting efficiency of 11.6%.

Geometry enhanced asymmetric rectifying tunneling diodes

In this article, the authors show that geometric asymmetry in the layout of tunnel diodes yields asymmetry in the current-voltage (I-V) relationships associated with these diodes. Asymmetry improves diode performance. This effect is demonstrated for polysilicon–SiO2–Ti/Au and for Ni–NiO–Ni tunneling structures. For a polysilicon–SiO2–Ti/Au asymmetric tunneling diode (ATD), sensitivity and I-V curvature improvements of 71% and 350% are achieved, respectively. For a Ni–NiO–Ni asymmetric diode, sensitivity and I-V curvature improvements of 15% and 39% are observed. The authors further demonstrate that this asymmetry enhances the microwave radiation detection sensitivity of these diodes at 900 MHz. Superior rectifying performance of a Ni ATD is observed due to smaller band-edge offsets in this material compared to that of a polysilicon ATD. The resulting structure can be further optimized using plasmonic field enhancement.

Fabrication of a thin film asymmetric tunneling diode using geometric field enhancement

We consider a metal-insulator-metal (MIM) diode as an infrared detector. Past research has successfully demonstrated the operation of these structures at infrared frequencies with an optimized antenna-coupling scheme [1–3]. Rectifying incident signals is essential for detection. The rectified DC voltage is proportional to the devices sensitivity, a figure of merit for tunneling diodes. Sensitivity is defined as the ratio of the second derivative to the first derivative of diode tunneling current (Γ7Γ) [4]. Therefore, increasing nonlinearity is the key point to improve performance. Furthermore, a significant asymmetry of tunneling current allows for unbiased detection of incident waves [3]. A general approach for highly nonlinear and asymmetric currents in MIM diodes is using geometrically dissimilar electrodes [3, 5]. In this report, we suggest a geometric field enhancement scheme to improve nonlinearity and asymmetry for tunneling currents. To demonstrate the concept, we fabricated a triangle pattern for one electrode, and the sharpest corner, which has a smallest angle, is covered by another metal electrode. Before the metallization, a thin surface oxide layer is formed on the triangle pattern using boiling water to make a MIM tunneling diode structure [6].

Design of radio frequency energy harvesting system for an unmanned airplane

Energy harvesting is a promising technique that can be used to drive various sorts of passively powered devices [1]. Viable energy sources include wind, sunlight, thermal energy, radio waves, mechanical vibration and so on. As an energy source existing ubiquitously in our environment, radio frequency (RF) energy harvesting has the potential to be widely applied. In this work, an RF energy harvesting system is described for the purpose of driving an unmanned airplane. Eventually, the airplane will be capable of remote recharge and become a self-powered system.

Antenna-coupled metal-insulator-metal tunneling diode for energy harvesting

Electromagnetic wave rectification is demonstrated at 6 and 17 GHz in an asymmetric unbiased metal-semiconductor-metal tunneling diode that uses geometric field enhancement and traps in the tunneling barrier.

Ultra-low power series pass element voltage regulator for RF-DC energy harvesting

Smart Dust motes or distributed sensor networks require sophisticated power supplies capable of storing energy for long periods of time, and delivering this energy slowly, on in bursts, during the life of the system. In addition, recharging would be a significant benefit — especially if this new charge could come from the network environment. RF beaming or scavenging is attractive. However, the input power of RF signal is relatively low leading to low charging voltages. Power management is likely to be a critical issue for such an approach [1]. Fig. 1 shows two stages of power management for a battery-driven supply in a mote device. In the standby mode, RF energy is easily captured by an antenna/rectifying system and this DC signal is converted to charge storage in the battery. In the active mode, the battery discharges through a voltage multiplier to obtain the necessary output voltage, which then is regulated using voltage regulator. This regulated output signal is supplied to any electronic system or mot. Above all, the required circuits should operate with low power dissipation. In Ref [2], a high energy density hybrid Ruthenium Oxide (RuO2.xH2O) galvanic cell is mentioned, and in Ref [3] low-power operation of switched-capacitor DC-DC converter is designed and tested. In this paper, single series pass element voltage regulators are designed and fabricated for charging the hydrated RuOx electrochemical cell.

Low leakage current technology in P+N silicon photodiode detector

Several applications of short wavelengths imaging detectors require low cost, large area, high energy resolution. The large area PIN photodiodes are fabricated for low noise amplifiers with as low as 1fA/cm2. Usually, the PIN diodes require high quality insulator without any defects and oxide charges [1]. In this work, we were able to reduce the leakage currents as low as 1nA/cm2 with various fabrication technologies mentioned below. The aim of this work was to fabricate silicon photodiode detector for specific wavelengths (λ=300~400nm). These devices are designed with relatively large active areas (~ 4cm2) for high voltage application while maintaining a low reverse leakage current density (~ 1nA/cm2). The low leakage currents are achieved by high temperature gettering process, shallow depth implantation, and floating guard ring structures.

Line-spike induced failure mechanism in integrated circuit bond-wires

A novel type of bond wire failure is described. In the present mechanism, the voltage line spikes are of such a short duration that they cannot propagate into the chip core circuits and cause internal failure. However, the induced spike is reflected back into the wire itself. It is shown that multiple spikes can propagate through interconnect lines and can result in constructive interference leading to a concentration of high power and thermal energy. The net effect is instantaneous melting of the associate bond-wire. Such induced spike trains are only observed in lines which are connected to ESD coupled diodes.