MEMS piezoelectric energy harvesters have captivated greater attention due to their advantages such as higher energy density, no need of external power, and ease of integration with other micro devices. It can capture the vibration energy of the environment to realize the self-powered micro and small power electronic devices. In this work, the influence of structural parameters on the performance of energy harvester is analyzed to improve the output voltage and efficiency. Three designs namely rectangle, single-stepped and double stepped rectangular microcantilevers are compared. Zinc oxide (ZnO) is used as a piezoelectric material because of its CMOS compatibility and eco-friendly nature. All the proposed structures are designed and analyzed using COMSOL Multiphysics. Among all the designs, double-stepped rectangular microcantilever gives an increased output voltage by 21,928.5

In this research, the effect of hydroxylamine (NH2OH) on the etching characteristics of sodium hydroxide (NaOH) is investigated. To perform this study, 12

Silicon wet bulk micromachining is an extensively used technique in microelectromechanical systems (MEMS) to fabricate variety of microstructures. It utilizes low-cost etchants and suitable for batch process that made it popular for industrial production. The etch rate and the undercutting at convex corner significantly affect the productivity. In wet anisotropic etching-based micromachining, Si{110} wafer is employed to fabricate unique shape geometries such as the microstructures with vertical sidewalls. In this research, we have investigated the etching characteristics of Si{110} in 10 M sodium hydroxide without and with addition of hydroxylamine (NH2OH). The main objective of the present work is to improve the etch rate and the undercutting at convex corners. Average surface roughness (R (a)), etch depth, and undercutting length are measured using a 3D scanning laser microscope. Surface morphology of the etched Si{110} surface is examined using a scanning electron microscope. The incorporation of NH2OH significantly improves the etch rate and the corner undercutting, which are useful to enhance the productivity. Additionally, the effect of etchant age on the etch rate and other etching characteristics are investigated. The etch rate of silicon and the undercutting at convex corners decrease with etchant aging. The results presented in this paper are very useful to scientists and engineers who use silicon wet anisotropic etching to fabricate MEMS structures using bulk micromachining. Moreover, it has great potential to promote the application of wet etching in MEMS.

Silicon wet bulk micromachining is an extensively used technique in microelectromechanical systems (MEMS) to fabricate variety of microstructures. It utilizes low-cost etchants and suitable for batch process that made it popular for industrial production. The etch rate and the undercutting at convex corner significantly affect the productivity. In wet anisotropic etching-based micromachining, Si{110} wafer is employed to fabricate unique shape geometries such as the microstructures with vertical sidewalls. In this research, we have investigated the etching characteristics of Si{110} in 10 M sodium hydroxide without and with addition of hydroxylamine (NH2OH). The main objective of the present work is to improve the etch rate and the undercutting at convex corners. Average surface roughness (R a), etch depth, and undercutting length are measured using a 3D scanning laser microscope. Surface morphology of the etched Si{110} surface is examined using a scanning electron microscope. The incorporation of NH2OH significantly improves the etch rate and the corner undercutting, which are useful to enhance the productivity. Additionally, the effect of etchant age on the etch rate and other etching characteristics are investigated. The etch rate of silicon and the undercutting at convex corners decrease with etchant aging. The results presented in this paper are very useful to scientists and engineers who use silicon wet anisotropic etching to fabricate MEMS structures using bulk micromachining. Moreover, it has great potential to promote the application of wet etching in MEMS.

In this work, deep grooves of more than 300 µm depth are fabricated in a high-quality Borofloat glass wafer using wet bulk micromachining in buffered HF (BHF) solution. The Cr/Au/photoresist layers are used as the etching mask. These masking layers showed very good chemical resistance to etching in BHF solution. The etchant provides smooth etched surface morphology with an excellent etch rate of 11.1 µm/min. The proposed process is very useful for the formation of deep grooves with smooth vertical sidewalls and uniform bottom surfaces.

Silicon wet bulk micromachining is the most widely used technique for the fabrication of diverse microstructures such as cantilevers, cavities, etc. in laboratory as well as in industry for micro-electromechanical system (MEMS) application. Although, increasing the throughput remains inevitable, and can be done by increasing the etching rate. Furthermore, freestanding structure release time can be reduced by the improved undercutting rate at convex corners. In this work, we have investigated the etching characteristics of a non-conventional etchant in the form of hydroxylamine (NH 2 OH) added sodium hydroxide (NaOH) solution. This research is focused on Si{100} wafer as this orientation is largely used in the fabrication of planer devices (e.g., complementary metal-oxide semiconductors) and microelectromechanical systems (e.g., inertial sensors). We have performed a systematic and parametric analysis without and with 12% NH 2 OH in 10 M NaOH for improved etching characteristics such as etch rate, undercutting at convex corners, and etched surface morphology. 3D scanning laser microscope is used to measure average surface roughness ( R a ), etch depth (d), and undercutting length ( l ). Morphology of the etched Si{100} surface is examined using optical and scanning electron microscopes. The addition of NH 2 OH in NaOH solution remarkably exhibited a two-fold increment in the etching rate of a Si{100} surface. Furthermore, the addition of NH 2 OH significantly improves the etched surface morphology and undercutting at convex corners. Undercutting at convex corners is highly prudent for the quick release of microstructures from the substrate. In addition, we have studied the effect of etchant age on etching characteristics. Results presented in this article are of large significance for engineering applications in both academic and industrial laboratories.

Silicon bulk micromachining is extensively employed method in microelectromechanical systems (MEMS) for the formation of freestanding (e.g., cantilevers) and fixed (e.g., cavities) microstructures. Wet anisotropic etching is a popular technique to perform silicon micromachining as it is low-cost, scalable, and suitable for large scale batch processing, which are the major factors considered in the industry to reduce the cost of the product. In this work, we report the wet anisotropic etching characteristics of Si{111} in sodium hydroxide (NaOH) without and with addition of hydroxylamine (NH2OH). 10M NaOH and 12% NH2OH are used for this study. The effect of NH2OH is investigated on the etch rate, etched surface roughness and morphology, and the undercutting at mask edges aligned along < 112 > direction. These are the major etching characteristics, which should be studied in a wet anisotropic etchant. A 3D laser scanning microscope is utilized to measure the surface roughness, etch depth, and undercutting length, while the etched surface morphology is examined using a scanning electron microscope (SEM). The incorporation of NH2OH in NaOH significantly enhances the etch rate and the undercutting at the mask edges that do not consist of {111} planes. To fabricate freestanding structure (e.g., microcantilever) on Si{111} wafer, high undercutting at < 112 > mask edges is desirable to reduce the release time. Moreover, the effect of etchant age on the abovementioned etching characteristics are investigated. The etch rate and undercutting reduce significantly with the age of the modified NaOH. The present paper reports very interesting results for the applications in wet bulk micromachining of Si{111}.

In the present work, we have studied the etching characteristics of Si{110} in 10M NaOH solution without and with addition of NH2OH. The etch rate of silicon and thermal oxide, and the undercutting rate at convex corners, which are important parameters to be known in the fabrication of MEMS structures using silicon wet bulk micromachining, have been studied in modified NaOH solution. The etch rate of silicon and the undercutting at convex corners increase significantly with the addition of NH2OH, while the etch rate of silicon dioxide reduces considerably with the addition of NH2OH etchant.

Wet anisotropic etching is extensively employed in silicon bulk micromachining to fabricate microstructures for various applications in the field of microelectromechanical systems (MEMS). In addition, it is most widely used for surface texturing to minimize the reflectance of light to improve the efficiency of crystalline silicon solar cells. In wet bulk micromachining, the etch rate is a major factor that affects the throughput. Slower etch rate increases the fabrication time and therefore is of great concern in MEMS industry where wet anisotropic etching is employed to perform the silicon bulk micromachining, especially to fabricate deep cavities and freestanding microstructures by removal of underneath material through undercutting process. Several methods have been proposed to increase the etch rate of silicon in wet anisotropic etchants either by physical means (e.g. agitation, microwave irradiation) or chemically by incorporation of additives. The ultrasonic agitation during etching and microwave irradiation on the etchants increase the etch rate. However, ultrasonic method may rupture the fragile structures and microwave irradiation causes irradiation damage to the structures. Another method is to increase the etching temperature towards the boiling point of the etchant. The etching characteristics of pure potassium hydroxide solution (KOH) is studied near the boiling point of KOH, while surfactant added tetramethylammonium hydroxide (TMAH) is investigated at higher temperature to increase the etch rate. Both these studies have shown a potential way of increasing the etch rate by elevating the temperature of the etchants to its boiling point, which is a function of concentration of etch solution. The effect of various kinds of additives on the etch rate of silicon is investigated in TMAH and KOH. In this paper, the additives which improve the etch rate have been discussed. Recently the effect of hydroxylamine (NH2OH) on the etching characteristics of TMAH and KOH is investigated in detail. The concentration of NH2OH in TMAH/KOH is varied to optimize the etchant composition to obtain improved etching characteristics especially the etch rate and undercutting which are important parameters for increasing throughput. In this article, different methods explored to improve the etch rate of silicon have been discussed so that the researchers/scientists/engineers can get the details of these methods in a single reference.

Wet bulk micromachining on Si{111} is done to fabricate simple to complex microstructures for applications in sensors and actuators. In this work, it has been performed a systematic study of Si{111} in modified 5 wt% tetramethyl-ammonium hydroxide (TMAH) with varying concentration of NH2OH for achieving improved etching characteristics especially high lateral undercutting at mask edges aligned along non-(110) directions. The concentration of NH2OH is varied from 5 to 20% in step of 5%. The lateral undercutting, which is highly desirable for the quick release of freestanding microstructures from the substrate, is increased considerably with the addition of NH2OH in TMAH solution. In addition, the incorporation of NH2OH improves etched surface morphology. Moreover, the effect of etchant ageing on the etching characteristics is investigated. Suspended microstructures are fabricated to demonstrate the application of modified TMAH solution for silicon wet bulk micromachining The results presented in this work are highly useful where Si{111} wafer is used for the fabrication of microstructures.

Recently the effect of hydroxylamine (NH2OH) on the etching characteristics of alkaline solution (e.g. potassium hydroxide (KOH) and tetramethylammonium hydroxide (TMAH)) is studied to obtain improved etching characteristics, especially high etch rate and enhanced undercutting at convex corners. Alkaline solution modified with NH2OH provides improved etch rate of silicon (Si), high etch selectivity between silicon and silicon dioxide (SiO2), considerably high undercutting at convex corner. As the addition of NH2OH alters the etching properties of alkaline solution dramatically, it is indispensable to investigate the effect of aging of NH2OH-added alkaline solution on its etching characteristics. In this work, the influence of aging of 15% NH2OH-added 20 wt% KOH, which is referred to as an etchant, on the etching characteristics of Si{100} and Si{110} is studied in detail. The results are systematically presented. The etch rate of silicon and the undercutting at convex corners decrease significantly with etchant aging at etching temperature, while the etch rate of silicon dioxide and etched surface morphology are not considerably affected with the age of the etchant. This study is significantly important for the researchers and industries where silicon wet anisotropic etching is used for silicon micromachining. (C) 2019 The Electrochemical Society.

Various process steps such as oxidation, diffusion, etching, lithography, etc. are employed for the fabrication of microstructures used in microelectromechanical systems (MEMS). In addition to these processes, micro-stereolithography (MSL), LIGA (a German acronym for Lithographie, Galvanoformung, Abformung), and micromachining are used in MEMS fabrication. Among these methods, micromachining is most widely used. It is further classified into two categories: surface micromachining and bulk micromachining. In these two techniques, bulk micromachining is a popular technique in MEMS fabrication and further divided into wet and dry bulk micromachining based on the type of chemical/process (wet chemical or gas/plasma/LASER) is employed. Wet anisotropic etching based micromachining is extensively used to fabricate various MEMS structures including suspended (e.g., microcantilever, diaphragm, etc.) and fixed (e.g., grooves, trenches, channels, etc.) structures. Wet anisotropic etching is used owing to its several benefits such as low cost, easy handling, orientation dependent etching, and bulk production capability over other techniques. Most importantly, it provides unique shape structures, which may not be possible by dry etching, for examples, the fabrication of freestanding microstructures using the undercutting process, slanted sidewalls for optical mirror application, etc. Tetramethylammonium hydroxide (TMAH) and potassium hydroxide (KOH) are the most widely employed etchants for silicon wet anisotropic etching. In these two etchants, TMAH is preferred when complementary metal oxide semiconductor (CMOS) compatibility is a major concern, and the oxide layer is used as a mask material. Although wet anisotropic etching has many advantages, industrial vii throughput is still limited due to the slow etch rate. In addition, slow etch rate increases the etching time and therefore mask material such as SiO2 is affected. Hence increasing the etch rate is an important research problem for both academic and industrial applications. In order to reduce the etching time to increase productivity, etchant must provide high etch rate. However, the etch rate attainable using the conventional etchants is limited and hence affects industrial productivity. Several methods have been proposed to increase the etch rate such as ultrasonic agitation and microwave irradiation during etching, adding some additives, oxidizing agents, various ion and non-ionic typed surfactants, etching at the boiling point of the etchant. Each method has its own pros and cons such as the ultrasonic method may rupture the fragile structures, and microwave irradiation causes damage. The present thesis work is focused on investigating a non-conventional etchant in the form of NH2OH-added in 5 wt% TMAH to determine its etching characteristics. A systematic and parametric analysis with concentrations of NH2OH varying from 5% to 20% in step of 5%, all in 5 wt% TMAH, to obtain the optimum concentration for achieving improved etching characteristics including higher etch rate, higher undercutting at convex corners, and smoother etched surface morphology is performed. To study different etching characteristics, various kinds of mask patterns are used on Si{100}, Si{110}, and Si{111} wafers. As the lower concentration TMAH (2-5 wt%) provides high etch in comparison to higher concentration TMAH (20-25 wt%), 5 wt% TMAH is selected to improve its etching characteristics. Average surface roughness (Ra), etch depth, and undercutting length are measured using 3D scanning laser microscope. Surface morphology of the etched surfaces is examined using a scanning electron microscope (SEM), and the thickness of the oxide layer is determined using spectroscopic ellipsometry. The etch rate of silicon with the addition of NH2OH in TMAH solution enhances viii significantly. Additionally, the incorporation of NH2OH significantly improves the etched surface morphology of Si{100} and the undercutting at the convex corner, which is highly desirable for the quick release of microstructures from the substrate. Moreover, the addition of NH2OH in TMAH increases etch selectivity between thermal oxide and silicon. 10% NH2OH is found to be an optimal concentration for addition in 5 wt% TMAH to achieve favorable etching characteristics. The optimal etchant composition (i.e., 10% NH2OH + 5 wt% TMAH) is used to study the effect of etchant age on the etching characteristics. Moreover, the effect of different concentrations of Triton in 10% NH2OH + 5 wt% TMAH is investigated. The etching mechanism in NH2OH-added alkaline solution is investigated. An in-depth analysis of possible etching mechanism in modified alkaline solutions is presented by considering NH2O- and OH- ions as catalysts and H2O as the reactive molecule. It accounts for the rise in etch rate in NH2OH-added alkaline solution. It also justifies the reasonable explanation of the etching mechanism in pure alkaline solution. In the fabrication of freestanding structures, the undercutting mechanism is used to remove the underneath material. In addition, it can be used to create a preetched pattern to determine precise crystallographic directions. In this work, a novel self-aligning pre-etched pattern to precisely identify the directions on Si{100} wafers is presented. The proposed pre-etched patterns self-align itself at the direction while becoming misaligned at directions away from the . This self-aligned pattern distinguishes the precise direction by making it appear quite obvious among the cluster of patterns. The aligned patterns can be easily located using a simple optical microscope. Additionally, the proposed technique does not require any measurement to identify the correct direction. ix In order to demonstrate the applications of NH2OH-added TMAH in MEMS fabrication, different kinds of suspended microstructures are fabricated successfully. Based on this study it can be stated that the NH2OH-added TMAH is an appropriate etchant composition for high speed silicon bulk micromachining for MEMS fabrication and therefore it is a potential candidate to replace pure TMAH for industrial applications. The results presented in this paper are extremely useful for engineering applications and will open a new direction of research for scientists in both academic as well as industrial laboratories.

In the present work, we have studied the etching characteristics of Si{100} and Si{110} in modified low concentration TMAH solution by adding different concentrations of NH2OH. The etch rate of silicon and thermal oxide, and etched surface morphology, which are important parameters to be known in the fabrication of MEMS structures using silicon wet bulk micromachining, have been studied in modified TMAH solution. In addition, the effect of aging time of the etchant solution on the etching characteristics is investigated.

In wet anisotropic etching based silicon bulk micromachining, undercutting, which has both advantage and disadvantage, takes place at the convex corners of microstructures. In order to retain the desired shape of fabricated structure, corner compensation method is most commonly used to protect the convex corners. The design and shape of the compensation geometry depend on the type of etchant. In this work, various types of corner compensating structures to protect convex corners on Si{110} and Si{110} are studied in potassium hydroxide (KOH) modified by adding NH 2 OH solution. Silicon etch rate in NH 2 OH-added KOH is 3-4 times more than that in pure KOH solution, which is very useful for industrial application to improve productivity. Mesa shape structures are fabricated using different shapes corner compensating geometry to optimize the design to obtain best shape convex corner. Triangular shape and beam shape geometries are found most appropriate structures to obtain well-shaped convex corner on Si{100} and Si{110}, respectively.

An aqueous tetramethylammonium hydroxide (TMAH) solution is widely used for silicon wet anisotropic etching to perform bulk micromachining for the fabrication of microstructures on a silicon wafer. To reduce the etching time to increase the productivity, etchant must provide high etch rate. In the present work, the etching characteristics of Si{110} in low concentration TMAH (5 wt%) with the addition of various concentrations (5–20%) of reducing agent hydroxylamine (NH2 OH) have been studied to increase the etch rate of Si{110} to reduce the etch time for the fabrication of microstructures. Moreover, it is aimed to enhance the undercutting at convex corner for the fast release of the structure. The etch rate of Si{110} and the undercutting at convex corners with the addition of NH2 OH increases by more than three times that in pure TMAH. In addition to the etch rate and undercutting, the effect of NH2 OH on etched surface morphology is investigated systematically. The present study is focused to enhance the application of wet etching in silicon micromachining for the fabrication of various kinds of microstructures for applications in microelectromechanical systems.

Silicon wet anisotropic etching based bulk micromachining technique is widely used for the fabrication of microelectromechanical systems components. In this technique of microfabrication, alignment of mask edges with crystallographic directions plays a crucial role to avoid unwanted undercutting to control the dimensions of fabricated structures. Various kinds of pre-etched designs have been reported to identify the crystallographic directions (e.g. 〈110〉 and 〈100〉) on Si{100} and Si{110} wafer surfaces. To the best of our knowledge, no pre-etched design has been reported to identify crystal directions on Si{111} wafer. In this work, a self-aligning technique based on pre-etched patterns has been investigated to precisely determine the 〈110〉 direction on Si{111} wafer surface. In this technique, a set of circular shape mask patterns close to wafer edge are etched for the identification of 〈110〉 direction. On wet anisotropic etching these patterns transform to hexagonal shapes. The notches of hexagonal patterns align precisely along a straight line only when they lie on exact 〈110〉 direction. The self-aligned notches can easily be identified by visual inspection using an optical microscope. The major advantages of this technique are simplicity, precision, and self-alignment. In addition, the pre-etched patterns at the wafer periphery occupy very less place.

Wet chemical etching is extensively used in the fabrication of microelectromechanical systems (MEMS) owing to its several benefits such as low cost, easy handling, and bulk production [1, 2]. TMAH and KOH are most widely employed etchants for silicon anisotropic etching. In these two etchants, TMAH is preferred when complementary metal oxide semiconductor (CMOS) compatibility is a major concern and the oxide layer is used as mask material [2, 3]. Etching behavior of TMAH can be modified by the incorporation of different kinds of additives such surfactants, alcohol, etc. [2-4]. Significant amount of research has been done to modify the etching characteristics by adding some additives, however very less is reported on TMAH-based ternary solutions. Present research reports the anisotropic etching characteristics of silicon in various concentrations of TMAH (5 wt%, 15 wt%, and 25 wt%) solutions containing 10% NH2OH and Triton-X-100 ranging from ppb to ppm level. The etch rate, undercutting at convex corners, and etched surface morphology are investigated in different compositions of ternary solutions (TMAH+NH2OH+Triton). Optical microscope, scanning electron microscope (SEM), and three-dimensional (3D) measuring laser microscope are employed for the characterization of etched surface morphology and to measure the etch depth and undercutting at convex corners. Figure 1 presents the etch rate of Si{100} and the undercutting rate (U <110> = l <110> /d, l <110>: undercutting length along <110> direction, d: etch depth) at convex corners. High etch rate and undercutting are achieved in NH2OH-added 15 wt% TMAH, while significantly less undercutting with reasonably good etch rate of Si{100} (Er = 18 µm/hr) is obtained in 25 wt% TMAH+10%NH2OH+1ppm Triton. The high undercutting is desirable when freestanding structures are fabricated, while it is unwanted effect when microstructures with convex corners have to be fabricated such as mesa structure. The present research is very useful for engineering applications for the fabrication of microstructures using CMOS-compatible silicon bulk micromachining for MEMS-based devices. References: [1] I. Zubel, M. Kramkowska, J. Micromech. Microeng. 1 5 485 (2004). [2] P. Pal, and K. Sato. J. Micromech.Microeng. 19 055003 (2009). [3] A. Ashok and P. Pal, Microsy. Technol. 1-8 (2015). [4] Y.W. Xu, A. Michael, C.Y. Kwok, Sens. Actuators A 166, 164-171 (2011). Figure 1