Papers by Krassimir Denishev
The resistive semiconducting metal oxide gas sensors currently constitute one of the most investi... more The resistive semiconducting metal oxide gas sensors currently constitute one of the most investigated groups of gas detecting device...
2019 IEEE 31st International Conference on Microelectronics (MIEL), 2019
In this study is presented technology for fabrication of a piezoelectric element as an alternativ... more In this study is presented technology for fabrication of a piezoelectric element as an alternative energy source (energy harvesting). The elements are produced on flexible polyethylene naphthalate (PEN) substrates and consist of novel lead-free nanocomposite [Ga-doped ZnO (GZO) - polyvinylidene fluoride (PVDF)]. The oxide film is deposited by vacuum radiofrequency (RF) sputtering and PVDF is pulverized by spray coating system. Aluminum and gold metal coatings are investigated as electrodes for optimal extraction of the generated electric energy from the piezoelectric coating. It was showed that PVDF spray deposition reduces the surface roughness of GZO film with 1.4 %. Piezoelectric response is measured at different applied dynamic loads with the two types of electrodes, as well as for oxide-only film. It was found that PVDF based composite leads to improved interface conditions for electrode coating, such as low parasitic capacitances. The highest obtained piezoelectric voltage is ~ 586 mV at 40 g mass weight load with frequency of 50 Hz for gold coated GZO+PVDF. This voltage is 41% higher and more stable in the time sweep in comparison with the case at PVDF-free piezoelectric film, and 29% higher than the composite element, but with aluminum electrode. The interface capacitance is 3 orders of magnitude lower (nF vs µF) and the contact resistance is 15 times smaller (Ω vs kΩ) when the interfaces are with gold, which optimizes the electric energy collection and enhances the energy harvesting performance.
IOP Conference Series: Materials Science and Engineering, 2019
In this study, lead-free, piezoelectric devices were fabricated by vacuum radiofrequency (RF) spu... more In this study, lead-free, piezoelectric devices were fabricated by vacuum radiofrequency (RF) sputtering of Ga–doped, ZnO (GZO) nanocoatings at different deposition modes on silicon substrates. Several deposition rates were varied (2 to 16 nm/min) by tuning the sputtering voltage and pressure, in order to control the microstructure and surface morphology of the films. The dependences of the piezoelectric properties of GZO thin films on the different deposition conditions were investigated. Significant dependency of the films’ microstructure and surface roughness was observed to the deposition modes used for fabrication. The results showed that after optimization, the surface roughness of the films grown using sputtering voltage 1.1 kV and Ar=2.5.10−2 Torr, is 6 nm. Films with such microstructures are characterized with crystallites orientation (002) and exhibit the highest piezoelectric coefficient of 96.3 pC/m, which is superior compared to other known, lead-free, piezoelectric mat...
ELECTRONICS’ 2005,21 – 23 September, 2005
In the human life, there are several areas, where chemical sensors are necessary. Such are medica... more In the human life, there are several areas, where chemical sensors are necessary. Such are medical care and analysis, breath analyzers, food control, wine aroma analysis, ecological air analysis, alcohol tests, technological gas and atmosphere analysis etc. In recent years, interest has grown in developing of an electronic "nose", capable of detecting mixed gases and even odors. There are several different ways to make such chemical sensors. One of them is to use chemical sensitive material to analyze the presence and the quantity of some gaseous component in the technological or surrounding atmosphere. In the last 5-10 years, in Micro Electro Mechanical Systems (MEMS), one of the most frequently used materials is Tin Oxide (SnO 2). This is semiconductor metal-oxide material, which change its surface and near surface conductivity, depending on the type and the quantity of the gaseous components of the atmosphere. It could be used for detecting very small quantities (ppm range) of such gases like CO, H 2 , NO, NO 2 , H 2 S, CH 4 , C 2 H 5 OH etc. There are different technological ways for creation of SnO 2 layers. They could be made using Thin Film Technologies (Vacuum Evaporation, Sputtering in Vacuum), Chemical Vapor Deposition, Thick Film Technologies (Screen Printing), Sol-Gel Process etc. Depending on the working temperature and the kind of impurities, these structures have different sensitivity and selectivity to different gases. Except gas-sensing layer, in the structure have to be included also a heating element and a temperature sensing element, like microhotplate (MHP).
In the human life, there are several areas, where chemical sensors are necessary. Such are medica... more In the human life, there are several areas, where chemical sensors are necessary. Such are medical care and analysis, breath analyzers, food control, wine aroma analysis, ecological air analysis, alcohol tests, technological gas and atmosphere analysis etc. In recent years, interest has grown in developing of an electronic "nose", capable of detecting mixed gases and even odors. There are several different ways to make such chemical sensors. One of them is to use chemical sensitive material to analyze the presence and the quantity of some gaseous component in the technological or surrounding atmosphere. In the last 5-10 years, in Micro Electro Mechanical Systems (MEMS), one of the most frequently used materials is Tin Oxide (SnO 2). This is semiconductor metal-oxide material, which change its surface and near surface conductivity, depending on the type and the quantity of the gaseous components of the atmosphere. It could be used for detecting very small quantities (ppm range) of such gases like CO, H 2 , NO, NO 2 , H 2 S, CH 4 , C 2 H 5 OH etc. There are different technological ways for creation of SnO 2 layers. They could be made using Thin Film Technologies (Vacuum Evaporation, Sputtering in Vacuum), Chemical Vapor Deposition, Thick Film Technologies (Screen Printing), Sol-Gel Process etc. Depending on the working temperature and the kind of impurities, these structures have different sensitivity and selectivity to different gases. Except gas-sensing layer, in the structure have to be included also a heating element and a temperature sensing element, like microhotplate (MHP).
Journal of Physics: Conference Series, 2014
Much effort is being applied to the development of autonomous Micro Electro Mechanical Systems (M... more Much effort is being applied to the development of autonomous Micro Electro Mechanical Systems (MEMS). In their full and total configuration, Microsystems consist of sensor part, data processing part and actuator part. One kind of actuator devices, these are Microfluidic Pumps. Nowadays, they find very large applications in different areas of life, science and techniques. Contemporary microelectronics and microelectronic technologies give the possibility to design and to produce Microfluidic Pumps, with very small dimensions and weight, low power consumption and very high reliability. In the present paper, an explanation of the principles of operation, technological ways of production and application are given. A Piezoelectric-driven Microfluidic Pump is designed and presented.
There are several possibilities for creating temperature sensors. Different principles and techno... more There are several possibilities for creating temperature sensors. Different principles and technological processes and sequences could be used. One of the simplest constructions is that, using thermocouples. In this case, different contact materials could be used. The choice is made by estimation of the chosen technology, the availability of technological equipment and materials, the application of the device, the parameters obtained by the sensor. In this case, a semiconductor sensor is designed. One of the materials, participated in the thermocouple is silicon (Si) of the base wafer. The second contact material is aluminum – Al, deposited as a metal layer. By serial connecting of several thermocouples (thermocouple sensor battery), it is possible to improve the efficiency of the device and to increase the output signal. Because of the necessity to have a big temperature difference between the hot and cold parts of the thermocouple, the designers have to reject the temperature cond...
A novel type of microactuator for linear displacements is presented. For the electrical to mechan... more A novel type of microactuator for linear displacements is presented. For the electrical to mechanical energy transformation it uses piezoelectric thin films. To produce linear displacement, this actuator uses a folded (meander-line geometry) path. The surface micromachining procedure is proposed. A particular set of dimensions is chosen and the actuator is designed. For quantitatively estimation of the performance of the actuator, an electromechanical model is developed and used. The results from the evaluation of the structure of meander-line actuator are shown. For producing the microactuator, fabrication procedures have been developed and presented. The technology sequence is in compliance with the standard CMOS technologies and could be performed together with some of them. The status of the fabrication efforts is given.
Gyroscope microelectromechanical systems (MEMS) are used in a wide spectrum of areas: aerospace i... more Gyroscope microelectromechanical systems (MEMS) are used in a wide spectrum of areas: aerospace industry, military, medicine, automotive industry and consumer electronics market with their dramatically reduced cost, size, and weight. This supposes a wide variety of design solutions, according to the gyroscope type, design style, MEMS technology, actuation mechanism, and coriolis sensor. The aim of this paper is to investigate, summarize and analyze the gyroscope MEMS design approaches and to provide a decision, suitable for the automotive applications.
2018 41st International Spring Seminar on Electronics Technology (ISSE), 2018
In this study BST thin films were RF sputtered on gold/polyethylene dioxithiophene coated polyeth... more In this study BST thin films were RF sputtered on gold/polyethylene dioxithiophene coated polyethylene naphthalate flexible substrate and piezoelectric generator with top patterned electrodes was designed. The composition of the films, piezoelectric response of the device, dielectric losses, capacity and mechanical stability were investigated. It was found that device consisting of barium strontium titanate (BST) films with thickness of 420 nm and composition of Ba0.5Sr0.5 TiO3, exhibited high capacity of 4.65 µF, low dielectric losses of 10−3℃10−2 in a broad range of frequencies and produced average voltage of 80 mV at applied low frequency vibrations with intensity of 350 g. The average produced power was 7.02 µW per bending cycle and the power density was ~2.34 µW/cm2. Maximal longitudinal piezoelectric coefficient d33 was found to be 10.8 pC/N The mechanical stability is satisfying, as the variation of the capacity was not greater than 17% up to 320 bending cycles, and the devic...
In the last 5-10 years, the high frequency (RF) applications of MicroElectroMechanical Systems (M... more In the last 5-10 years, the high frequency (RF) applications of MicroElectroMechanical Systems (MEMS) devices have reached significant progress, because of their low price, technology, matched with the ordinary microelectronic technologies, good RF parameters and yield. The process of research, investigation and design of RF MEMS switch are presented. The results from this process, in connection with the design of ordinary RF coplanar transmission line, interrupted RF coplanar transmission line and their combination with a contacting metal electrode are shown.
2017 15th International Conference on Electrical Machines, Drives and Power Systems (ELMA), 2017
This work reports about the fabrication of piezoelectric energy harvesting with ZnO nanostructure... more This work reports about the fabrication of piezoelectric energy harvesting with ZnO nanostructure grown on polymeric based electrode. The piezoelectric film exhibits nanobranched morphology, which provide favorable conditions for dipoles orientation and thus the device is characterized with relatively low dielectric losses in the range of 0.4–3.9×10−2 and piezoelectric voltage of 3.8V at 4.8 kg mechanical loading. The minimum weight at which piezoelectric reaction arises is 3 gr, corresponding to generated piezoelectric voltage of 200mV.
The electromagnetic force that is most commonly used in microactuators is not the only driving fo... more The electromagnetic force that is most commonly used in microactuators is not the only driving force. A MEMS variable capacitor could be driven by vertical thermal actuators. Thermal actuators can generate relatively large force and displacement at low actuating voltage. The MEMS capacitor is created by using surface micromachining. The power consumption and low switching frequency are concerns for applications with thermal actuators. Although, unlike variable capacitors driven electrostatically, using thermal actuators undesired electrostatic actuation is avoided.
The tactile sensors are widely used in the areas of robotics, human identification etc. Especiall... more The tactile sensors are widely used in the areas of robotics, human identification etc. Especially in human identification, the biometric data of person could be used as input data. By using sensors, the physical parameters of the shape of the ear, the iris of eye, the shape of the hand, the image of veins, fingerprints etc. could be obtained and processed. The most widely used method of identification and biometric sign of the person is the tactile processing. In Micro Electro Mechanical Systems (MEMS), piezoresistive sensors could be designed and built by using elements with different shapes, such as bridges, cantilevers, membranes. A Micromechanical Piezoresistive Tactile Sensor has been successfully designed. With the aim to be compatible with the current technological processes in microelectronics, the technological sequence for manufacturing of this device includes some of the typical standard processes for making of Selfaligned Polysilicon Unipolar Transistors and Integrated ...
Materials, methods & technologies, 2018
In this paper, we demonstrate fabrication of environmental friendly flexible piezoelectric genera... more In this paper, we demonstrate fabrication of environmental friendly flexible piezoelectric generator and propose optimization strategy for its performance by a formation of stress concentrators in the piezoelectric material. The entire structure is characterized with improved electrical response to mechanical stimuli, although the thickness of the used piezoelectric film is in nanosized range. Piezoelectric oxide films are grown by vacuum sputtering and patterned in a specific way by applying lift-off microfabrication technology. The design is based on simulation analysis, showing a concentration of peak stress in specific areas, causing enhanced charge generation. As a result, the piezoelectric coefficient of 11.28 pC/N is achieved and it is superior, compared to the device without concentrators. This value is competitive to devices using lead-containing lead zirconium titanate (PZT), as well as to devices with millimeter thickness of the piezoelectric material. Vibrational dynamic...
2021 XXX International Scientific Conference Electronics (ET)
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Papers by Krassimir Denishev