In-situ plasma chamber monitoring for feedforward process control

This paper examines the effects of polymer buildup in plasma etching systems and describes a micromachined sensor for in-situ polymer thickness measurement. Using gas flows of 45 sccm CHF3CHF3 and 15 sccm CF4CF4 at 50 mTorr and 1000 W, the oxide:polysilicon selectivity ranges from 2.6 to 8.5 as the polymer thickness on the tool walls varies from 0 to 240 nm. The polymer sensor is based on an electrothermal oscillator that measures the thermal mass change as polymer builds up on a stress-compensated dielectric window. The change in the thermal mass of the window can be detected as a variation in the pulse width (cooling time) of the oscillation. The device operates with a typical cooling time of 2.7 msec and has a measurement resolution of better than 1 nm. The device is flush-mounted in the chamber wall with the exposed window area protected by a thin film of iridium against damage by the plasma. © 1998 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87553/2/427_1.pd

A self-controlled microcontrolled microvalve

Integrated microvalves are needed for a broad range of semiconductor-processing-related applications. These include precision mass microflow controllers (μFCs) for dry etch systems, miniature gas chromatography systems for real-time monitoring, point-of-use semiconductor process reactant generators, and compact control systems for mini-environments. This paper reports a pneumatically actuated, integrated silicon microvalve, which was developed as a forerunner to an 8b μFC intended for the precision control of semiconductor process gases in the range from 0.1 to 10 sccm. The structure was designed to be batch-fabricated and compatible with on-chip thermopneumatic actuation. Assembled single-bit μFC devices achieve the targeted flow rate of 5 sccm (determined by an in-line flow channel) at 20 psid (1034 torr). The valve alone may achieve significantly higher flow rates. The leak rate is 0.08 sccm under 26.1 psig actuation pressure, and the valve can seal against pressures greater than 29 psid (1500 torr). © 1998 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87556/2/937_1.pd

A high-performance microflowmeter with built-in self test

This paper reports the development of a high-performance readout scheme based on a switched-capacitor circuit and intended for use with an ultrasensitive microflowmeter. The microflow transducer improves significantly on the resolution of current flow devices and uses a differential capacitive pressure sensor to measure the flow. The readout electronics feature a clocking speed of 100 kHz and can drive loads as high as 35 pF. The high d.c. gain of the circuit topology (75 dB) is relatively insensitive to stray input capacitance and is ideally suited for a multichip sensor realization. The uncompensated linearity of the overall readout circuit is 10 bits and the pressure/flow resolution is 12 bits. Since ultrasensitive membranes respond to electrostatic forces, the output is characterized as a function of the duty cycle and pulse width of the readout clocking waveforms. The membrane does not respond to these waveforms for high frequencies ( > 50 kHz), but for lower frequencies the diaphragm deflects in response to the time-average voltage applied across the device. A self-test mode can therefore be implemented simply by changing the duty cycle of this pulse. By modifying the amplitude of the waveform, the device can be autocalibrated over a limited pressure range. The transducer and circuitry have been integrated into a flow package, and the multichip device has been tested versus a calibrated gas flow.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30918/1/0000588.pd

A scaled electronically-configurable multichannel recording array

This paper describes a multichannel microelectrode array capable of recording single-unit neural activity in the central nervous system. The probe features 32 recording sites on a scaled shank less than 50,[mu]m wide. On-chip CMOS circuitry implements signal amplification, multiplexing, and selftesting on eight active channels selected from among the 32 sites. The circuitry has a power dissipation of 3 mW, an active area of 2.5 mm2, and requires only three external leads. It utilizes bidirectional signal transmission over the output data lead for signal output and for channel selection.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27927/1/0000351.pd

Flexible miniature ribbon cables for long-term connection to implantable sensors

This paper describes the development of miniature, multi-lead ribbon cables for connecting implantable sensors to host electronics, either implanted or in the external world. The cables are flexible, electrically stable and biocompatible. Two technologies have been developed: one using polyimide (DuPont PI-2555) and the other using silicon as the support material. The present cables are less than 200 [mu]m wide, are 10 to 20 [mu]m thick and can be of arbitrary length (typically 1-2 cm). They can support as many leads as desired and can be bonded to the sensor substrate using flip-chip bonding techniques.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28664/1/0000481.pd

Active positioning device for a perimodiolar cochlear electrode array

The authors report on an actuated positioning device for a cochlear prosthesis insertion procedure. The device consists of multiple high-aspect ratio fluidic actuator chambers integrated with a high-density silicon cochlear electrode array and manufactured in a tapered-helix form. Actuation chambers with cross-sectional sizes as small as 40 × 200 μm and lengths of 30 mm have been fabricated using flexible polymers. The device will allow for low-resistance basilar insertion of a stimulating electrode array into the cochlea providing for deep, perimodiolar position considered most beneficial for auditory nerve stimulation, while minimizing intracochlear trauma. Experimental measurements, FEA analysis, and modeling demonstrate a viable and appropriate actuation method for a cochlear implant procedure.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47852/1/542_2004_Article_376.pd

Integrated sensors: interfacing electronics to a non-electronic world

This paper considers the rapidly-developing field of integrated sensors, in which one or more transducers are joined with custom interface circuitry on a single chip. Many of the issues confronting continued development in this are discussed, including process compatibility and circuit partitioning. Backed by an increasingly powerful array of solid-state process technologies, integrated sensors are expected to be widely applied to extend microcomputer-based control in a variety of areas.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24532/1/0000811.pd

A bulk silicon SOI process for active intevated sensor

This paper reports a process for the formation of very high quality single-crystal silicon films on glass substrates. The process utilizes the electrostatic bonding of silicon and glass wafers, with subsequent etching of the silicon to form siliconon-insulator (SOI) films having thicknesses controlled from less than 2.[mu]m to over 20,[mu]m with better than 10% uniformity. The use of Corning type 1729 glass substrates yields an excellent thermal expansion match to the silicon film and allows the use of post-bond processing temperatures as high as 850 [deg]C, permitting the formation of both transducer and transistor structures in the film after bonding and etch-back. Thus, the process offers one means of integrating MOS or bipolar circuitry into dissolved-wafer sensing structures. MOS devices formed in such films show characteristics similar to those in standard bulk silicon, including n-channel mobilities of 640 cm2/V s, the highest ever reported for SOI on glass. A variety of related processes are also possible, where some or all of the high-temperature silicon device processing is performed before bonding to the glass substrate.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28489/1/0000284.pd

Process alternatives and scaling limits for high-density silicon tactile imagers

In this paper the process complexities and parasitic substrate coupling effects are compared for several different high-density capacitive tactile imagers. The dissolved-wafer process using diffused bulk-silicon row lines and metal-on-glass columns is found to offer the simplest process and fastest response, requiring only five non-critical masks and producing a settling time for the column charge of about 1 [mu]s. Using this process, a 1024-element array with a force range of 1 gm and a spatial resolution of 500 [mu]m produces a force resolution equivalent to seven bits. Scaled to a 4096-element array, this same process should produce a force resolution of nearly six bits for the same force range and a spatial resolution of 250 [mu]m.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28661/1/0000478.pd

Low-temperature silicon wafer-to-wafer bonding using gold at eutectic temperature

Micromechanical smart sensor and actuator systems of high complexity become commercially viable when realized as a multi-wafer device in which the mechanical functions are distributed over different wafers and one of the wafers is dedicated to contain the readout circuits. The individually-processed wafers can be assembled using wafer-to-wafer bonding and can be combined to one single functional electro-mechanical unit using through-wafer interconnect, provided that the processes involved comply with the constraints imposed by the proper operation of the active electrical and micromechanical subsystems. This implies low-temperature wafer-to-wafer bonding and through-wafer interconnect. Au/Si eutectic bonding has been investigated as it can conveniently be combined with bulk-micromachined through-wafer interconnect. The temperature control in eutectic bonding has been shown to be critical.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31608/1/0000537.pd