This paper describes a 2-20 GHz 6-bit True-Time Delay. A total equivalent electrical length in air of 43.5 mm (145 ps) is achieved over a 2-20 GHz bandwidth. Digital drivers and a serial-to-parallel converter are integrated on the same MMIC. The ED02AH 0.2 µm PHEMT process from OMMIC is used. The time delay elements are real-ised using constant-R networks. The three smallest bits make use of a self-switched version of the constant -R networks while the 3 largest bits use a topol-ogy with single-pole double-throw (SPDT) switches and constant-R networks in the delay path. Measurement results for a typical chip are presented.

The effects of the SiN layer normally used to passivate and protect the exposed junction surfaces in InP/InGaAs heterojunction bipolar transistors have been studied and shown to degrade the transistor properties. These effects are ascribed primarily to surface damage associated with the high SiN deposition temperature (350 °C). A degradation of the emitter-base properties was observed through the nonideal behavior of the base current and the measured short minority-carrier lifetime in the base, extracted by using the base width modulation method. Degradation in the current gain and emitter injection efficiency was also observed. A clear recovery of the transistor was observed after removing the SiN passivation layer indicating that the high SiN deposition temperature results in a high-surface-state density which increases the surface recombination velocity and degrades the junction properties. It is concluded that a low-temperature deposition and good quality dielectric are necessary to exploit the excellent electrical properties of InP-based heterojunction bipolar transistors.

The noise properties at room temperature of multiwalled carbon nanotubes under forward bias, for frequencies between 10 Hz–10 kHz, have been investigated. The noise measurements were made for one individual multiwalled carbon nanotube (1 MW) and two crossing multiwalled carbon nanotubes (2 CMW). The excess noise found in 1 MW is consistently 1/f-like. However, 2 CMW shows higher noise level, and the noise spectrum has an unusual dependence on the current. The main origin of noise in 2 CMW was attributed to the diffusion noise.

The effect of plasma etching on the noise properties of Ti/p-Si and Ti/p-Si1−xGex (with x=0.05) Schottky junctions has been investigated. The noise measurements were performed over a temperature range of 77–300 K at frequencies of 10–100 kHz. The main noise source observed in these diodes during argon plasma sputter etching was attributed to the generation–recombination noise. From the analysis of the noise data, we have determined the interface state density and evaluated the introduced damage. The results indicate two optimum operating temperatures where low-noise level can be achieved. Furthermore, the activation energies of trap levels have been extracted by using noise spectroscopy (NS) and compared with those measured by deep-level transient spectroscopy (DLTS). We found two additional trap states using NS not detected by DLTS measurements. Finally, a noise comparison between Ti/p-Si and Ir/p-Si fabricated on an unetched substrate has been made.

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