John A. Yasaitis

High-performance, tensile-strained Ge p-i-n photodetectors on a Si platform

We demonstrate a high-performance, tensile-strained Ge p-i-n photodetector on Si platform with an extended detection spectrum of 650–1605 nm and a 3 dB bandwidth of 8.5 GHz measured at λ=1040nm. The full bandwidth of the photodetector is achieved at a low reverse bias of 1 V, compatible with the low driving voltage requirements of Si ultralarge-scale integrated circuits. Due to the direct bandgap shrinkage induced by a 0.20% tensile strain in the Ge layer, the device covers the entire C band and a large part of the L band in telecommunications. The responsivities of the device at 850, 980, 1310, 1550, and 1605 nm are 0.55, 0.68, 0.87, 0.56, and 0.11A∕W, respectively, without antireflection coating. The internal quantum efficiency in the wavelength range of 650–1340 nm is over 90%. The entire device was fabricated using materials and processing that can be implemented in a standard Si complementary metal oxide semiconductor (CMOS) process flow. With high speed, a broad detection spectrum and compatibility ...

Electrostatic charge and field sensors based on micromechanical resonators

We have developed highly sensitive electrometers and electrostatic fieldmeters (EFMs) that make use of micromechanical variable capacitors. Modulation of the input capacitance, a technique used in macroscale instruments such as the vibrating-reed electrometer and the field-mill electrostatic voltmeter (ESV), moves the detection bandwidth away from the 1/f-noise-limited regime, thus improving the signal-to-noise ratio (SNR). The variable capacitors are implemented by electrostatically driven resonators with differential actuation and sensing to reduce drive-signal feedthrough. The resonators in the electrometer utilize a balanced comb structure to implement harmonic sensing. Two fabrication methods were employed - a hybrid technology utilizing fluidically self-assembled JFETs and SOI microstructures, and an integrated process from Analog Devices combining 0.8-/spl mu/m CMOS and 6-/spl mu/m-thick polysilicon microstructures. All devices operate in ambient air at room temperature. Measured data from one electrometer with an input capacitance of 0.7 pF indicates a charge resolution of 4.5 aC rms (28 electrons) in a 0.3 Hz bandwidth. The resolution of this electrometer is unequaled by any known ambient-air-operated instrument over a wide range of source capacitances. The EFM has a resolution of 630 V/m, the best reported figure for a MEMS device.

A modular process for integrating thick polysilicon MEMS devices with sub-micron CMOS

A new MEMS process module, called Mod MEMS, has been developed to monolithically integrate thick (5-10um), multilayer polysilicon MEMS structures with sub-micron CMOS. This process is particularly useful for advanced inertial MEMS products such as automotive airbag accelerometers where reduced cost and increased functionality is required, or low cost, high performance gyroscopes where thick polysilicon (>6um) and CMOS integration is required to increase poly mass and stiffness, and reduce electrical parasitics in order to optimize angular rate sensing. In this paper we will describe the new modular process flow, development of the critical unit process steps, integration of the module with a foundry sub-micron CMOS process, and provide test data on several inertial designs fabricated with this process.

Structure of Amorphous Silicon Monoxide

The pair distribution function in amorphous deposited silicon monoxide has been measured at room temperature. The result is not in good agreement with expectations for a mixture of well‐defined amorphous silicon and amorphous SiO2. Other possibilities, for which the average number of nearest‐neighbor Si–O bonds per atom deviates significantly from 2, can be ruled out. A ring‐type structure, consistent with the diffraction results, and also (apparently) with optical data, is suggested as the most likely alternative.

Silicon-based highly-efficient fiber-to-waveguide coupler for high index contrast systems

A coupler to efficiently transfer broadband light from a single-mode optical fiber to a single-mode high-index contrast waveguide has been fabricated on a silicon substrate. We utilized a novel coupling scheme, with a vertically asymmetric design consisting of a stepwise parabolic graded index profile combined with a horizontal taper, to simultaneously confine light in both directions. Coupling efficiency has been measured as a function of the device dimensions. The optimal coupling efficiency is achieved for structures whose length equals the focal distance of the graded index and whose input width is close to the mode field diameter of the fiber. The fabricated structure is compact, robust and highly efficient, with an insertion loss of 2.2dB at 1550nm. The coupler exhibits less than 1dB variation in coupling efficiency in the measured spectral range from 1520nmto1620nm. The lowest insertion loss of 1.9dB is measured at 1540nm. The coupler design offers highly efficient coupling for single mode waveguid...

Modal Coupling in Micromechanical Vibratory Rate Gyroscopes

The authors present modeling approaches to describe the coupling of modes in a resonant vibratory rate gyroscope. Modal coupling due to off-diagonal stiffness and damping terms is considered. Three analytical modeling approaches are presented in the context of a z-axis micromechanical vibratory rate gyroscope fabricated in an integrated polysilicon surface-micromachining process. The first approach is based on frequency-response analysis of the gyroscope output. The second approach takes the route of state-space-based system identification to identify the modal-coupling parameters. A third approach based on measured vibration data identifies the coupling parameters due to stiffness and damping. These three methods are then applied to predict the extent of displacement and force coupling between the drive and the sense axes of an existing device as a function of varying degrees of matching between the resonant frequencies associated with the drive and the sense modes. Experimental data show that as the resonant frequencies of the drive and sense modes are brought closer together, an improvement in overall resolution and scale factor of the device is obtained at the expense of an enhanced coupling of forces to displacements between the two axes and the onset of instability for an open-loop sensing implementation

A double-polysilicon self-aligned npn bipolar process (ADRF) with optional NMOS transistors for RF and microwave applications

A silicon bipolar process for RF and microwave applications, which features 25-GHz double-polysilicon self-aligned npn bipolar transistors with 5.5-V BV/sub CEO/, optional 0.7-/spl mu/m NMOS transistors with p/sup +/ polysilicon gate for switch applications, lateral pnp transistors, high and low valued resistors, and p/sup +/ polysilicon-to-n/sup +/ plug capacitors, is described. The npn transistors utilize nitride-oxide composite spacers formed using sacrificial TEOS spacers. The RF and microwave capabilities of the process up to several GHz are demonstrated by fabricating and characterizing RF amplifiers, low noise amplifiers, and RF switches.

High performance asymmetric graded index coupler with integrated lens for high index waveguides

The authors have demonstrated a planar, monolithically integrated lensed, asymmetric graded index fiber-to-waveguide coupler with 0.45dB coupling loss at 1550nm. The silicon-based coupler and the waveguides were fabricated entirely by complementary metal-oxide semiconductor compatible processes. They also observed an excellent broadband performance between 1520 and 1630nm. The average coupling loss was 0.4dB across the entire cathodoluminescence band (1530–1625nm).

Low resistance laser formed lateral links

A new technique is described for reliably forming low resistance links by using a laser to bridge a lateral gap between two Al conductors deposited on insulating polysilicon. Resistances in the range of 1-10 ohms were achieved for gap widths of approximately 2-3 microns using 1 msec pulses from an argon laser. This technique should be ideally suited to implementing defect avoidance using redundancy in large RAMs and complex VLSI circuits. It requires a single level of metal and should provide higher density and lower capacitance when compared to alternative techniques.

High performance Ge p-i-n photodetectors on Si

We demonstrate a high performance Ge p-i-n photodetector on Si platform with an extended detection spectrum of 650-1605 nm, a 3 dB bandwidth of 8.5 GHz, and a responsivity of 0.68 A/W, measured at /spl lambda/ = 1040 nm.