V. Milanovic

Characterization of broad-band transmission for coplanar waveguides on CMOS silicon substrates

This paper presents characteristics of microwave transmission in coplanar waveguides (CPWs) on silicon (Si) substrates fabricated through commercial CMOS foundries. Due to the CMOS fabrication, the metal strips of the CPW are encapsulated in thin films of Si dioxide. Many test sets were fabricated with different line dimensions, all on p-type substrates with resistivities in the range from 0.4 /spl Omega//spl middot/cm to 12.5 /spl Omega//spl middot/cm. Propagation constant and characteristic impedance measurements were performed at frequencies from 0.1 to 40 GHz, using a vector-network analyzer and the through-reflect-line (TRL) deembedding technique. A quasi-TEM equivalent circuit model was developed from the available process parameters, which accounts for the effects of the electromagnetic fields in the CPW structure over a broad frequency range. The analysis was based on the conformal mapping of the CPW multilayer dielectric cross section to obtain accurate circuit representation for the effects of the transverse fields.

Micromachined microwave transmission lines in CMOS technology

Coplanar waveguides were designed and fabricated through a commercial CMOS process with post-processing micromachining. The transmission-line layouts were designed with commercial computer-aided design (CAD) tools. Integrated circuits (ICs) were fabricated through the MOSIS service, and subsequently suspended by top-side etching. The absence of the lossy silicon substrate after etching results in significantly improved insertion-loss characteristics, dispersion characteristics, and phase velocity. Two types of layout are presented for different ranges of characteristic impedance. Measurements of the waveguides both before and after micromachining were performed at frequencies from 1 to 40 GHz using a vector network analyzer and de-embedding techniques, showing improvement of loss characteristics of orders of magnitude. For the entire range of frequencies, for the 50-/spl Omega/ layout, losses do not exceed 4 dB/cm. These losses are mainly due to the small width and thickness of the metal strips. Before etching, losses are as high as 38 dB/cm due to currents in the underlying substrate. Phase velocity in the micromachined transmission lines is close to that in free space.

Thermoelectric power sensor for microwave applications by commercial CMOS fabrication

This work describes an implementation of a thermoelectric microwave power sensor fabricated through commercial CMOS process with additional maskless etching. The sensor combines micromachined coplanar waveguide and contact pads, a microwave termination which dissipates heat proportionally to input microwave power, and many aluminum-polysilicon thermocouples. The device was designed and fabricated in standard CMOS technology, including the appropriate superimposed dielectric openings for post-fabrication micromachining. By removing the bulk silicon located beneath the device through micromachining, thermal and electromagnetic losses are minimized. The sensor measures signal true RMS power in the frequency range up to 20 GHz with input power in the -30 dBm to +10 dBm range. Over this 40 dB dynamic range, output voltage versus input power is linear within less than /spl plusmn/0.16%. Automatic network analyzer data show an acceptable input return loss of less than -30 dB over the entire frequency range.

CMOS foundry implementation of Schottky diodes for RF detection

Schottky diodes for RF power measurement were designed and fabricated using a commercial n-well CMOS foundry process through the MOSIS service. The Schottky diodes are implemented by modifying the SCMOS technology file of the public-domain graphics layout editor, MAGIC, or by explicitly implementing the appropriate CIF layers. The modifications allow direct contact of first-layer metal to the low-doped substrate. Current-voltage measurements showed that only the n-type devices had rectifying properties with a barrier height of 0.78 eV. The I-V results were verified by performing capacitance-voltage measurements on diodes of different contact-areas. The diodes were tested in an RF detector circuit. The cut off frequency of the detector was shown to be 600 MHz.

Micromachined thermocouple microwave detector by commercial CMOS fabrication

This paper reports on the design and testing of a thermocouple microwave detector fabricated through a commercial CMOS foundry with an additional maskless etching procedure. The detector measures true r.m.s. power of signals in the frequency range from 50 MHz to 20 GHz, and input power range from -30 to +10 dBm, the device has linearity better than /spl plusmn/0.4% for input power versus output voltage over the 40 dB dynamic range. Measurements of the return loss, obtained using an automatic network analyzer, show acceptable input return loss of less than -20 dB over the entire frequency range. The sensitivity of the detector was measured to be (1.007/spl plusmn/0.004) mV/mW.

Micromachined coplanar waveguides in CMOS technology

Coplanar waveguides were fabricated in standard complimentary metal-oxide semiconductor (CMOS) with postprocessing micromachining. ICs were designed with commercial CAD tools, fabricated through the MOSIS service, and subsequently suspended by maskless top-side etching. Absence of the lossy silicon substrate after etching results in significantly improved insertion loss characteristics, dispersion characteristics, and phase velocity. Measurements were performed at frequencies from 1 to 40 GHz, before and after micromachining. These show improvement in loss characteristics of orders of magnitude. For the micromachined line, loss does not exceed 4 dB/cm. Before etching, loss as high as 38 dB/cm is measured. Phase velocity /spl Gamma//sub p//spl ap/0.8/spl middot/c is achieved for the micromachined line.

Implementation of thermoelectric microwave power sensors in CMOS technology

This paper presents two implementations of efficient thermoelectric microwave power sensors fabricated through commercial CMOS processes with additional maskless etching. Two types of thermocouple detectors were fabricated and tested. Both types measure true rms power of signals in the frequency range up to 20 GHz and input power range from -30 dBm to +10 dBm. The devices have linearity better than /spl plusmn/0.4% for output dc voltage vs. input microwave power over this 40 dB dynamic range. Measurements obtained using an automatic network analyzer show an acceptable input return loss of less than -20 dB over the entire frequency range.

Design and fabrication of micromachined passive microwave filtering elements in CMOS technology

This paper describes a novel implementation of micromachined microwave resonators and filters, coupled with low-loss transmission lines, fabricated in standard CMOS technology. Selective etching of the Si substrate beneath the microwave elements results in significantly lowered transmission loss, improved quality factor and operating frequency range. This allows operation at gigahertz frequencies. Resonators with Q-factors of 20 and resonant frequencies of 2 GHz and 21 GHz are reported which are significant results for standard CMOS technology. A low-pass filter is also reported with a 2.5 GHz cutoff frequency. The resonant and cutoff frequencies are in general adjustable within the 1 to 40 GHz band. These devices are useful for integration with microwave power sensors, and have application in wireless communication systems where low-loss operation above 1 GHz is essential.

Synchronization of chaotic neural networks for secure communications

Methods for synchronizing discrete time chaotic neural networks are presented with applications in secure communications. Chaotic neurons, characterized with a piecewise linear transfer function, are connected into Hopfield-like networks. The networks are used as transmitter and receiver in chaotic communications. The first algorithm is a modification of simple chaotic masking which makes synchronization robust and insensitive to the perturbation from the added information signal. A mathematical proof and simulation results of the scheme are shown for small networks. We have verified the method experimentally, using single-neuron circuits. The second algorithm utilizes modulation of the transmitting chaotic network and detection of the corresponding synchronization error at the receiver.

Micromachined thermocouple microwave detector in CMOS technology

This paper presents the design and testing of a thermocouple microwave power detector fabricated through a commercial n-well CMOS foundry with an additional maskless etching procedure. The detector measures true r.m.s. power of signals in the frequency range from 50 MHz to 20 GHz, and input power ranging from -30 dBm to +10 dBm. The device has linearity better than /spl plusmn/0.4% for output vs. input power over the 40 dB dynamic range. Measurements of the return loss, obtained using an automatic network analyzer, show an acceptable input return loss of less than -20 dB over the entire frequency range. The sensitivity of the detector was measured to be (1.328/spl plusmn/0.004) mV/mW.