Linear thermal expansion measurements have been carried out from 6 to 340 K on a high-purity silicon sample using a linear absolute capacitance dilatometer. The accuracy of the measurements varies from ±0.01×10−8 K−1 at the lowest temperatures to ±0.1×10−8 K−1 or 0.1%, whichever is greater, near room temperature, and is sufficient to establish silicon as a thermal expansion standard for these temperatures. The agreement with previous data is satisfactory at low temperatures and excellent above room temperature where laser-interferometry data of comparable accuracy exist. Thermal expansions calculated from ultrasonic and heat-capacity data are preferred below 13 K where experimental problems occurred.

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The chemical-vapor deposition conditions for the growth of pure boron (PureB) layers on silicon at temperatures as low as 400°C were investigated with the purpose of optimizing photodiodes fabricated with PureB anodes for minimal B-layer thickness, low dark current and chemical robustness. The B-deposition is performed in a commercially-available Si epitaxial reactor from a diborane precursor. In-situ methods commonly used to improve the cleanliness of the Si surface before deposition are tested for a deposition temperature of 450°C and PureB layer thickness of 3 nm. Specifically, high-temperature baking in hydrogen, and exposure to HCl are tested. Both material analysis and electrical diode characterization indicate that these extra cleaning steps degrade the properties of the PureB layer and the fabricated diodes.

Figure 1. Unit Cells for (a) LC model and (b) TC model "catches-up." This phenomenon is known as edge sharpening [5], [6].Popular NLTL designs use a reverse-biased Schottky barrier as the nonlinear capacitance. Because the leakage current from a large area junction introduces intolerable shunt losses, NLTLs are often constructed as "artificial" transmission lines using an LC lattice [3]. Noting that the unit cell of the lattice, Fig.l (a), is a low-pass filter, it follows that the NLTL will exhibit a cutoff frequency, called the Bragg frequency, which corresponds to a phase shift of 180 0 per stage. Like any lowpass filter, if a step edge with bandwidth greater than f B is applied to the input of the lattice, one can observe time domain ringing at the output. In the case of the NLTL, ringing can be observed even when the input bandwidth is smaller than f B due to the edge sharpening property of the line. This phenomenon was observed in simulations in early NLTL work [7], and is generally avoided by designing the Bragg frequency to be much higher than the cutoff frequency of the varactor diodes.Unlike the linear case where ringing is characteristic of high frequency energy being rejected by the filter, the nonlinearity of the NLTL is capable of transferring significant energy from the input signal into the Bragg mode. The conversion is not harmonic; the frequency of the ringing depends on the structure of the NLTL and amplitude of the input. It is power efficient and temperature stable in the sense that the NLTL is a passive structure and does not require DC bias currents for active elements. Further, ringing approaching the amplitude of the input may be obtained with relatively few stages. III. MODELING AND IMPLEMENTATIONWhen designing a practical NLTL in an MMIC environment, the inductance is implemented as a segment of conventional transmission line and the physical structure is closer to the transmission line-capacitor (TC) model of Fig. 1(b). Because the LC model is easier to work with, analysis is usually restricted to the long-wavelength regime, modeling the Abstract-Nonlinear transmission lines (NLTL) have received considerable attention for their frequency conversion, fast pulse generation, and rise/falltime compression properties. Here we present a new mode of operation for the NLTL which uses falltime compression to generate short RF pulses near the Bragg cutoff frequency. While this phenomenon has been reported in circuit model simulations, we demonstrate, to our knowledge, its first experimental verification. We demonstrate control of the pulse center frequency using next-nearest neighbor coupling and examine the feasibility of MMIC implementation. Our resulting devices generate short microwave pulses suitable for short range wireless communication. The frequency conversion is non-harmonic and requires no active bias currents.

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Nonlinear transmission lines (NLTLs) are used in diverse applications such as edge-sharpening, pulse generation, and frequency conversion, however, length of a useful NLTL can require significant MMIC or RFIC real estate. We present an analytical model for the complex propagation constant of lossy, distributed NLTLs and fabricate several NLTLs in 0.25µm CMOS for verification. Space-saving layout techniques such as serpentine folding and floating-grid substrate shielding are fabricated and we examine their impact on the edge-sharpening performance of the NLTLs.