Marko Pavlin

Capacitive pressure sensors realized with LTCC technology

This work is focused on pressure sensors designed as a ceramic capsule consisting of a circular edge-clamped deformable diaphragm, which is bonded to the rigid ring, and the ring is fixed on the base substrate. These three elements form the cavity of the pressure sensor. The capacitive pressure sensor is based on changes of the capacitance values between two electrodes. One thick-film electrode is deposited on the diaphragm and the other on the rigid substrate. The distance between electrodes and the area of electrodes define the initial capacitance of the capacitive pressure sensor, and together with the geometry and flexibility of the diaphragm define the sensitivity of the sensor. The diaphragm with the diameter of 9 mm made with low-temperature cofired ceramic (LTCC) has a thickness of 200 mum and the distance between electrodes is about 70 mum. The initial capacitance is around 10 pF. The capacitive ceramic pressure sensor is the part of the electronic conditioning circuit with the frequency output. The typical output frequency is about 10 kHz and sensitivities are between 2.5 and 3.5 Hz/kPa.

Packaging technologies for pressure‐sensors

Pressure‐sensor miniaturization requires high‐density packaging. This means that designers are constantly faced with all kinds of challenging, and sometimes impossible, requirements. In this paper we will present three examples with specific technologies and aspects of miniaturization and packaging. The first example is a pressure switch, the second a pressure sensor and the third a smart pressure sensor.

Vertical thick-film resistors as load sensors

Abstract A vertical thick-film resistor for a fine-pitch-array load sensor has been developed. This sensor can be used for measuring the relief (footprint) of a load force. The thick-film resistor, with a sheet resistivity of 1 Mohm/sq., is vertically oriented and terminated with a conductive layer at the bottom and on the top of the resistor layer. Sensitivity to the load (pressure) is based on the piezoresistive effect of the thick-film resistor. The experimental work on the sensing element resulted in a vertical resistor with a resistance of 2500 ohm and a sensitivity (dR/R) of about 1.3% at 6 bar pressure. Because of high density and large number of sensing elements, the whole system is divided into a number of segments. Each segment integrates 16 sensing elements (vertical thick-film resistors), 16 diodes, and 16 terminals for the inter-segment connections.

Ceramic MEMS Designed for Wireless Pressure Monitoring in the Industrial Environment

This paper presents the design of a wireless pressure-monitoring system for harsh-environment applications. Two types of ceramic pressure sensors made with a low-temperature cofired ceramic (LTCC) were considered. The first type is a piezoresistive strain gauge pressure sensor. The second type is a capacitive pressure sensor, which is based on changes of the capacitance values between two electrodes: one electrode is fixed and the other is movable under an applied pressure. The design was primarily focused on low power consumption. Reliable operation in the presence of disturbances, like electromagnetic interference, parasitic capacitances, etc., proved to be contradictory constraints. A piezoresistive ceramic pressure sensor with a high bridge impedance was chosen for use in a wireless pressure-monitoring system and an acceptable solution using energy-harvesting techniques has been achieved. The described solution allows for the integration of a sensor element with an energy harvester that has a printed thick-film battery and complete electronics in a single substrate packaged inside a compact housing.

Silicon pressure sensors with a thick film periphery

Silicon piezoresistive pressure sensor dies are mounted on a ceramic substrate where the signal conditioning electronics are implemented in thick film technology. In this paper some of these techniques, e.g. special attachment and bonding requirements, methods for temperature compensation, the principles of parameter adjustment, and encapsulation, are presented. For illustration two examples are described. The first is a multipoint monitoring system with 720 measuring points in a test mattress. The second example is a family of industrial pressure transducers.

Some results obtained with diffusion patterning technology

Diffusion patterning is a dielectric patterning technology, which is used in the screen printed thick film technology for higher density multilayer circuits. This technology is suitable for producing lower cost multichip modules and requires a low additional investment in conventional thick film technology production lines. Comparisons of via resolution capability of diffusion patterning versus conventional thick film technology are described and discussed. Preliminary experimental results obtained with a test circuit showed that 200μm lines and 200μm vias could be achieved with acceptable yield and with minimal modification to standard production lines. The electronic circuit for the pressure sensor was designed and realised with the verified technology as a low‐cost ceramic multichip module. A few results of an investigation of some thick film materials, which comprise the “set” of pastes for diffusion patterning technology, are presented.

Towards noninvasive bioimpedance sensor design based on wide bandwidth ring resonator

Miniature and noninvasive sensors play a major role in healthcare, by monitoring vital health parameters in real time. Furthermore, energy efficiency is an important issue in human-centric embedded systems. In this paper we describe a new approach for a contact-less bioimpedance measurement. The basic idea stems from the permittivity measurement of electronic circuit substrate. A common procedure in this case is to design and fabricate a substrate with a given resonator structure where the dielectric constant can be calculated from the measured resonant frequency and known resonator geometry and substrate thickness. Similar principle can be employed for bioimpedance measurement. The resonator can be designed such that the resonant frequency lies within the responsive range of the target tissue where the resonant frequency changes are highest following physiological processes. The changed value of the frequency reflects the dielectric properties of the target object. The measured frequency thus implicitly reflects biological and physiological processes within the target object. Some preliminary experiments are described in this paper.

A Wireless Interface for Replacing the Cables in Bridge-Sensor Applications

This paper presents a solution in which a wireless interface is employed to replace the cables in bridge-sensor measurement applications. The most noticeable feature of the presented approach is the fact that the wireless interface simply replaces the cables without any additional hardware modification to the existing system. In this approach, the concept of reciprocal topology is employed, where the transmitter side acquires signals with its own transfer function and the receiver side reconstructs them with the transfer function reciprocal to the transmitter transfer function. In this paper the principle of data acquisition and reconstruction is described together with the implementation details of the signal transfer from the sensor to the signal-monitoring equipment. The wireless data communication was investigated and proprietary data-reduction methods were developed. The proposed methods and algorithms were implemented using two different wireless technologies. The performance was evaluated with a dedicated data-acquisition system and finally, the test results were analyzed. The two different sets of results indicated the high level of amplitude and the temporal accuracy of the wirelessly transferred sensor signals.

Thick Film Interconnections for Sensor Applications

Signal processing for some sensor applications demands circuits with specific characteristics, such as miniaturization, high functional density, high number of input ports, and high signal speed. For some sensors operating in industrial environments protection from electromagnetic interference (EMI) is also required. Thick film technology is convenient way to realize such circuits, but some special technological processes must be used. In this paper some of these will be presented through some examples of thick film multilayer hybrids. First is the multipoint pressure measuring system for medical applications. It is designed for measuring 720 pressure points in a test mattress for hospital patients. The second example is thick film multilayer interconnections for sensor array readout with high function density, high signal speed, and low interlayer capacitances. The third example is of thick film hybrid circuits for proximity switches.