Particle Sensor Using Solidly Mounted Resonators

This paper describes the development of a novel particle sensing system employing zinc oxide based solidly mounted resonator (SMR) devices for the detection of airborne fine particles (i.e., PM2.5 and PM10). The system operates in a dual configuration in which two SMR devices are driven by Colpitts-type oscillators in a differential mode. Particles are detected by the frequency shift caused by the mass of particles present on one resonator with while the other acts as a reference channel. Experimental validation of the system was performed inside an environmental chamber using a dust generator with the particles of known size and concentration. A sensor sensitivity of 4.6 Hz per μg/m3 was demonstrated for the SMRs resonating at a frequency of 970 MHz. Our results demonstrate that the SMR-based system has the potential to be implemented in CMOS technology as a low-cost, miniature smart particle detector for the real-time monitoring of airborne particles

Monolithic Integration Piezoelectric Resonators on CMOS for Radio-Frequency and Sensing Applications

Software cognitive radios and Internet of Things (IoT) are recent interest areas that need low loss and low power consumption hardware. More specifically, the area of software cognitive radios requires that hardware be frequency agile and highly selective. Meanwhile, IoT relies on multiple low power sensor networks. By combining Complementary Metal Oxide Semiconductors (CMOS) technology with piezoelectric Micro-Electro-Mechanical Systems (MEMS), we can fabricate Systems-on-Chip (SoC) that can be used as filters or references (oscillators) and highly selective sensors. In this work we developed a die-level compatible process for the monolithic integration of Bulk Acoustic Resonators (BAWs) on CMOS for low power, reduced area and high-quality passives for radio frequency applications. Using CMOS as a fabrication substrate some stringent requirements were added to maintain the dies and the technology’s integrity. A few of these limitations were the need for a low thermal budget fabrication process, die handling and electro-static discharge (ESD) protection. The devices were first fabricated on glass for modeling extraction that was later used for the design of the integrated circuits (IC). Three integrated circuits were designed as substrates for the integration using IBM’s 180nm and TSMC’s 65nm technology. A monolithic BAW oscillator with a resonance frequency of 1.8GHz was demonstrated with an FOM ~186dBc/Hz, comparable to other academia work. Using the developed process, a membrane BAW structure (FBAR) was integrated as well. Using a susceptor coating and zinc oxide’s (ZnO) high temperature coefficient of frequency (TCF) the device was studied as an alternative uncooled infrared sensor. Finally, a reprogrammable IC and an RF PCB were designed for volatile organic compound (VOC) testing using self-assembled monolayers (SAMs) as the absorber layer

Low voltage acoustic particle velocity sensor with integrated low noise chopper pre-amplifier

Novel acoustic particle velocity (APV) sensors suitable for low voltage, battery-powered systems are proposed. The sensing structure consists of four silicide polysilicon wires placed over suspended dielectric membranes and arranged in a Wheatstone full-bridge configuration. The device has been fabricated combining a commercial CMOS process with a simple and low cost post-processing technique. An ultra low noise chopper pre-amplifier has been integrated on the same chip. Preliminary noise and acoustic characterization is presented

CMOS compatible solidly mounted resonator for air quality monitoring

Air pollution has become a growing concern around the world. Human exposure to hazardous air pollutants is associated with a range of health problems and increased mortality. An estimated 40,000 early deaths per year are caused by the exposure to air pollutants in the UK alone, which cost over £20 billion annually to individuals and health services1. In this work, novel solidly mounted resonator (SMR) devices were developed for integration in a low-cost, portable air quality monitor for the real-time monitoring of particulate matter and volatile organic compounds (VOCs). Finite element models of the SMRs were developed to aid their design and simulate the response of the sensors to particles and exposure to VOCs. For particle sensing, a SMR based unit was developed, working in a dual mode configuration. The unit was characterised inside an environmental chamber, together with commercial reference instruments, to particles of known size and composition. A detection limit of 20 μg/m3 was found (below the safe exposure limit). To target fine particles (<2.5 μm), a virtual impactor was incorporated into the system. For VOC detection, the SMR devices were functionalised with polymer coatings to detect acetone and toluene vapours (most common VOCs in air). A polymer drop-coating system was developed to complete this aim (polymer film thicknesses <100nm). An automated VOC test station was developed to characterise the SMR based sensors to low ppm concentrations of the target vapours (<200 ppm). The SMR devices demonstrated a limit of detection of 5 ppm to toluene and 50 ppm of acetone (well below the safe exposure limits). A novel CMOS based SMR device, suitable for volume production and monolithic integration, was designed with an integrated microheater and CMOS acoustic mirror. The heater was included to vary the temperature of the sensing area (to enhance the sensitivity of the SMR to a particular VOC through temperature modulation or to clear particles off the surface). The fabricated device (1.9 GHz) exhibited good performance

Microelectromechanical Systems and Devices

The advances of microelectromechanical systems (MEMS) and devices have been instrumental in the demonstration of new devices and applications, and even in the creation of new fields of research and development: bioMEMS, actuators, microfluidic devices, RF and optical MEMS. Experience indicates a need for MEMS book covering these materials as well as the most important process steps in bulk micro-machining and modeling. We are very pleased to present this book that contains 18 chapters, written by the experts in the field of MEMS. These chapters are groups into four broad sections of BioMEMS Devices, MEMS characterization and micromachining, RF and Optical MEMS, and MEMS based Actuators. The book starts with the emerging field of bioMEMS, including MEMS coil for retinal prostheses, DNA extraction by micro/bio-fluidics devices and acoustic biosensors. MEMS characterization, micromachining, macromodels, RF and Optical MEMS switches are discussed in next sections. The book concludes with the emphasis on MEMS based actuators

Characterization and modeling of CMOS-compatible acoustical particle velocity sensors for applications requiring low supply voltages

Acoustic particle velocity sensors have been obtained applying simple low resolution micromachining steps to chips fabricated using a standard microelectronic process. Each sensor consists of four silicided polysilicon wires, suspended over cavities etched into the substrate, and connected to form a heatstone bridge. Full compatibility of the micromachining procedure with the original process is demonstrated by integrating a simple pre-amplifier on the same chip as the sensors and showing that both blocks are functional. Proper design of the sensing structures allows them to operate with a single 3.3 V power supply. Sensitivity and noise measurements, performed to estimate the sensor detection limit, are described. Excess noise with a flicker-like behavior, not ascribable to the amplifier, is found when the bridges are biased in working conditions. In addition, the dependence of the sensitivity on the dc bias voltage of the bridges is investigated, comparing the experimental data with the results of a simple analytical model and finite element method simulations

Thermally modulated solidly mounted resonators for air quality monitoring

The effect of air pollution on the environment and human health is a cause of major concern. Each year millions of deaths are attributed to poor air quality, and it is estimated that its economic cost runs into the trillions of pounds. Especially the pollutant particulate matter has been identified as one of the main contributors to poor health. Hence there is much activity that attempts to reduce the concentration of small particles in air. To better understand the effect of particulate matter on the world and for the effective mitigation of the problems it causes and exacerbates, it is necessary to acquire reliable air quality data. Readily available particle sensing equipment is thus required to expand existing air quality monitoring systems that can deliver meaningful results. To this end, a range of particle sensing technologies have been studied. Resonator particle sensors based on microelectromechanical systems are one promising example of this because of their potential to provide an affordable solution that can be mass manufactured and use very little power or space compared to many currently available particle monitoring devices. In this thesis a novel particle sensor based on a solidly mounted resonator with an integrated microheater that is compatible with a standard integrated circuit fabrication process is developed and tested experimentally. The main objective of this work is to demonstrate for the first time that temperature modulation applied to a solidly mounted resonator could increase its sensitivity to particles, while targeted particle deposition could increase the effective sensitivity of the system to aerosolised particles and that the application of both could thus help to make this type of sensor more suitable for real world air quality monitoring applications. The design of the sensor is based upon a complementary metal oxide semiconductor process that includes the deposition of a piezoelectric bulk acoustic wave resonator on top of the standard layer stack. It is verified in an extensive set of simulations and the fabricated sensor is subsequently characterised. In the characterisation study the resonator had a resonant frequency around 2 GHz and a Q factor of approximately 200. The device was found to be capable of handling temperatures induced through the application of an electric current to the integrated microheater of up to 598 K. Experimentally the device’s resonant frequency, S-parameter value and its temperature for different applied currents were found to be within approximately 6 % of the sensor simulations. A custom particle test rig was built to evaluate the sensors performance as a particle sensor. One of the main obstacles remaining with these types of sensors is the reliability of particle measurements, which is reduced by difficulties to achieve repeatable particle sampling. To resolve this issue a thermophoretic particle deposition channel was added to a commercial FBAR device and experimental tests were carried out that showed it could reduce the variation in measurement results between repeat tests from 71 % to 14 %. The novel solidly mounted resonator particle sensor device was tested inside the particle test rig and found to have a sensitivity to particle deposition of approximately 40 Hz/ng. Temperature modulation was applied to the sensor through the integrated microheater and this was found to increase the sensitivity of the device by a factor of almost five to 190 Hz/ng. It also reduced the sensor’s detection limit from approximately 100 ng to 50 ng. The thermophoretic microchannel was added and found to approximately double the sensitivity of the novel sensor to airborne particles through increased particle sampling efficiency. The novel thermally modulated SMR particle sensor was found to have significant potential for low-cost quality monitoring applications