Wen H. Ko

Touch mode capacitive pressure sensors

Touch mode capacitive pressure sensors offer better performance in industrial applications than other devices. In touch mode operation, the diaphragm of the capacitive pressure sensor touches the substrate structure in operation range. The advantages of this mode of operation are near-linear output characteristics, large over-range pressure and robust structure that make it capable to withstand harsh industrial field environment. The principle, design, and characteristics of touch mode capacitive pressure sensors using various materials and technologies are discussed in this paper.

A Wireless and Batteryless 10-Bit Implantable Blood Pressure Sensing Microsystem With Adaptive RF Powering for Real-Time Laboratory Mice Monitoring

An implantable real-time blood pressure monitoring microsystem for laboratory mice has been demonstrated. The system achieves a 10-bit blood pressure sensing resolution and can wirelessly transmit the pressure information to an external unit. The implantable device is operated in a batteryless manner, powered by an external RF power source. The received RF power level can be sensed and wirelessly transmitted along with blood pressure signal for feedback control of the external RF power. The microsystem employs an instrumented silicone cuff, wrapped around a blood vessel with a diameter of approximately 200 ¿m, for blood pressure monitoring. The cuff is filled by low-viscosity silicone oil with an immersed MEMS capacitive pressure sensor and integrated electronic system to detect a down-scaled vessel blood pressure waveform with a scaling factor of approximately 0.1. The integrated electronic system, consisting of a capacitance-to-voltage converter, an 11-bit ADC, an adaptive RF powering system, an oscillator-based 433 MHz FSK transmitter and digital control circuitry, is fabricated in a 1.5 ¿m CMOS process and dissipates a power of 300 ¿W. The packaged microsystem weighs 130 milligram and achieves a capacitive sensing resolution of 75 aF over 1 kHz bandwidth, equivalent to a pressure sensing resolution of 1 mmHg inside an animal vessel, with a dynamic range of 60 dB. Untethered laboratory animal in vivo evaluation demonstrates that the microsystem can capture real-time blood pressure information with a high fidelity under an adaptive RF powering and wireless data telemetry condition.

High-temperature single-crystal 3C-SiC capacitive pressure sensor

Single-crystal 3C-silicon carbide (SiC) capacitive pressure sensors are proposed for high-temperature sensing applications. The prototype device consists of an edge-clamped circular 3C-SiC diaphragm with a radius of 400 /spl mu/m and a thickness of 0.5 /spl mu/m suspended over a 2-/spl mu/m sealed cavity on a silicon substrate. The 3C-SiC film is grown epitaxially on a 100-mm diameter <100> silicon substrate by atmospheric pressure chemical vapor deposition. The fabricated sensor demonstrates a high-temperature sensing capability up to 400/spl deg/C, limited by the test setup. At 400/spl deg/C, the device achieves a linear characteristic response between 1100 and 1760 torr with a sensitivity of 7.7 fF/torr, a linearity of 2.1%, and a hysterisis of 3.7% with a sensing repeatability of 39 torr (52 mbar). A wide range of sensor specifications, such as linear ranges, sensitivities, and capacitance values, can be achieved by choosing the proper device geometrical parameters.

Residual stress and mechanical properties of boron-doped p+-silicon films

Abstract Annealing was used to relax non-uniform tensile stress in boron-doped p + -Si cantilever beams. The optimum annealing condition was determined. A for

Wireless Batteryless Implantable Blood Pressure Monitoring Microsystem for Small Laboratory Animals

A novel, wireless, batteryless, implantable blood pressure monitoring microsystem for small laboratory animals is developed for advanced biological and system biology research. The system employs an instrumented elastic circular cuff, wrapped around a blood vessel, for real-time blood pressure monitoring. The elastic circular cuff is made of soft bio-compatible silicone material, which is filled with bio-compatible insulating fluid with an immersed microelectromechanical systems (MEMS) pressure sensor and integrated electronic system to detect a down-scaled vessel blood pressure waveform. This technique avoids vessel penetration and substantially minimizes vessel restriction due to the soft cuff elasticity, thus attractive for long-term monitoring. A large-model engineering experiment is first developed to verify and demonstrate the concept. A miniature prototype monitoring cuff is then fabricated and implanted in two laboratory rats to evaluate its functionality. A wireless and batteryless monitoring microsystem is then implanted and characterized in a laboratory rat. The measured in vivo blood pressure waveform by the microsystem and a reference waveform recorded by a commercial catheter-tip transducer are closely matched in shape with a constant scaling factor, demonstrating a blood pressure signal with high fidelity can be wirelessly obtained by the implantable monitoring microsystem. The overall implant dissipates 300 ¿W, which is powered by an external adaptive RF powering source.

A High-Performance MEMS Capacitive Strain Sensing System

This paper describes a high-performance strain sensing microsystem. The system consists of four parallel differential MEMS capacitive strain sensors with a nominal capacitance value of 440 fF, converting an input strain to a capacitance change with a sensitivity of 265 aF per microstrain (muepsiv), and low-noise integrated sensing electronics, which employ a differential continuous-time synchronous detection architecture converting the capacitive signal to an output voltage for further signal processing. Based on system noise characterization, the prototype design shows a capability of measuring a strain resolution of 0.9 nepsiv/radicHz, while demonstrating a maximum dc input stain range of 1000 muepsiv. The overall system consumes 1.5 mA dc current from a 3-V supply

Modeling of touch mode capacitive sensors and diaphragms

The understanding of deflection, stress and strain of thin diaphragms with clamped edges under various loads including when the diaphragm touches the substrate is of great importance for designing and fabricating sensors and actuators. This article reports the finite element analysis (FEA) of these diaphragms for computer-aided design of touch mode capacitive pressure sensors. The advantages of the touch mode operation are good linearity in touched range, mechanically robust and large overload protection. These simulation results predict the change of the performance when the device parameters are varied and can be served as a design tool to arrive at a set of desired performance. The results also are useful for designing actuators with diaphragms.

Touch mode capacitive pressure sensors for industrial applications

The principle, simulation, design, characteristics and application of touch mode capacitive pressure sensors for industrial applications, including embedded monitoring of tire pressure are presented. In touch mode operation, the diaphragm of the capacitive pressure sensor touches the substrate structure. The advantages of touch mode of operation are: near linear output, large over-range pressure and robust structure that make it capable to withstand harsh industrial field environment. When properly packaged, the device can be used to measure fluid now, force, acceleration, and displacement, etc. in industrial applications.

Intracranial Pressure Telemetry System Using Semicustom Integrated Circuits

A new generation of implantable, telemetric transmitters for intracranial pressure (ICP) measurements have been developed. A unique technique used in packaging the silicon piezoresistive pt essure transducer provides excellent long-term stability. Pulse code modulation is used for data transmission over a radio frequency (RF) link. To minimize the component count, two semicustom, bipolar integrated circuits are used. The transmitter electronics are housed inside a 29 ×20 ×7 mm titanium package along with the pressure transducer and two lithium batteries. Even though the transmitter consumes less than 0.4 mW of power, it is turned on remotely via RF signal transduction only on demand in order to extend the lifetime of the batteries to years. The pressure input of the transmitter has a dynamic range of ¿100- +200 mmHg with a 0.3 mmHg resolution and a 1 mmHg accuracy. Long-term in vitro and in vivo pressure baseline stabilities of better than 1 and 2 mmHg per month, respectively, have been achieved.

Theoretical modeling of boundary conditions in microfabricated beams

The authors report detailed modeling of step-up boundary conditions in surface micromachined beams and investigate their effects on the onset of buckling in doubly supported beams. Both cantilever and doubly supported beams are considered. Finite element analysis is used to accurately model the mechanical behavior of the step-up boundary conditions. An extended beam model which uses equivalent torsional and axial stiffnesses in conjunction with a simply supported boundary condition is developed to account for the finite stiffness of a step-up boundary condition. The finite element results are used to calculate the values of the equivalent stiffnesses of the extended beam model for practical geometries of step-up boundary conditions. The extended beam model is used to calculate buckling loads for doubly supported beams. Equivalent stiffness values for torsional and axial springs are for geometries of practical importance to microelectromechanical systems.<<ETX>>