Vinod Kumar Khanna

New‐generation nano‐engineered biosensors, enabling nanotechnologies and nanomaterials

Purpose – This paper aims to discover the novelties in biosensor fabrication brought about by breakthroughs in nanomaterials and process techniques, the resulting enhancement in biosensor functionalities, new applications and future possibilities.Design/methodology/approach – The impact of nanotechnology on biosensor advancement has been examined. Different directions of biosensor research in the nano era have been highlighted. These include the efforts made through nanotechnology to improve the performance parameters of the existing biosensors, and for implementation of innovative biosensor concepts.Findings – Nanotechnology is a key technology in biosensor development. It has permeated into the biosensor field and brought in its wake far‐reaching changes.Practical implications – Biosensor science and engineering are central to virtually all aspects of life including medical diagnostics, environmental monitoring and biotechnological process control. Therefore, the progress in biosensors brought about by ...

Carrier lifetimes and recombination-generation mechanisms in semiconductor device physics

The existence of a multiplicity of carrier lifetimes and their inextricable linkage to the measurement technique, injection level and position of the recombination centre in the forbidden energy gap presents difficulties in the teaching of this key semiconductor parameter controlling the performance of semiconductor devices such as diodes, transistors, insulated gate bipolar transistors, thyristors and solar cells. This paper points out that in the teaching of carrier lifetime in semiconductor device courses, the types of lifetime, their physical significance and underlying recombination?generation mechanisms should be introduced and the correlation of each lifetime with the terminal property of the semiconductor device should be highlighted. The use of a particular method for measurement of the relevant lifetime and the injection level of carriers chosen should be explained. The paper provides an update on the important considerations about carrier lifetimes which need to be stressed by the teacher.

Design and Fabrication of Si-Diaphragm, ZnO Piezoelectric Film-Based MEMS Acoustic Sensor Using SOI Wafers

This paper reports a simpler technique for fabricating an microelectromechanical system acoustic sensor based on a piezoelectric zinc oxide (ZnO) thin film, utilizing silicon-on-insulator wafers. A highly c-axis-oriented ZnO film of thickness 2.4 μm, which is covered with 0.2-μm-thick PECVD SiO2, is sandwiched between two aluminum electrodes on a 25- μm-thick silicon diaphragm. This diaphragm thickness has been optimized to withstand sound pressure level range of 120-160 dB. Stress distribution studies using ANSYS have been performed to determine the locations for placement of capacitor electrodes. This paper also reports a technique for the creation of a positive slope of the ZnO step to ensure proper coverage during Al metallization. In order to maximize yield, process steps have been developed to avoid the microtunnel blockage by silicon/glass particles. The packaged sensor is found to exhibit a sensitivity of 382 μV/Pa (RMS) in the frequency range from 30 to 8000 Hz, under varying acoustic pressure.

Short-Channel Effects in MOSFETs

Short-channel effects are a series of phenomena that take place when the channel length of the MOSFET becomes approximately equal to the space charge regions of source and drain junctions with the substrate. They lead to a series of issues including polysilicon gate depletion effect , threshold voltage roll-off , drain-induced barrier lowering (DIBL) , velocity saturation , reverse leakage current rise, mobility reduction, hot carrier effects , and similar other annoyances. Mitigation of the problem posed by polysilicon gate depletion effect via restoration of metal gate structure is presented. Threshold voltage reduction makes it difficult to turn the transistor off completely. By DIBL effect, electrostatic coupling between the source and drain makes the gate ineffective. Velocity saturation decreases the current drive. The leakage current increases the power dissipation. Enhanced surface scattering degrades the mobility of charge carriers affecting the output current. Apart from these factors, impact ionization and hot carrier effects seriously impair the MOSFET performance and cause the device to diverge in behavior from long-channel ones. Notable solutions are the gate oxide thickness cutback, use of high-κ dielectrics, strain engineering, etc. Nevertheless, the various effects mentioned severely downgrade the performance of planar CMOS transistors at process nodes <90 nm.

Fabrication and characterisation of Al gate n-metal–oxide–semiconductor field-effect transistor, on-chip fabricated with silicon nitride ion-sensitive field-effect transistor

In the present study, temperature drift analysis of metal–oxide–semiconductor field-effect transistor (MOSFET) is carried out using silicon nitride/SiO2 as dielectric film. An n-channel depletion-mode MOSFET was fabricated with silicon nitride ion-sensitive field-effect transistor (ISFET) on the same wafer. The study presents the fabrication, simulation and characterisation of MOSFET. The gate of the ISFET is stacked with silicon nitride/SiO2 sensing membrane that was deposited using low pressure chemical vapour deposition. Output and transfer characteristics of on-chip fabricated Al gate MOSFET were obtained in order to study the fabricated ISFET behaviour to be used as pH sensor. Silicon nitride is preferred over SiO2 sensing film/dielectric (in case of MOSFET) which has better sensitivity and low drift. Process and device simulations were performed using Silvaco® TCAD tool.

ZnO Etching and Microtunnel Fabrication for High-Reliability MEMS Acoustic Sensor

This paper describes a technique for uniform step coverage of aluminum metal (Al) on ZnO film in the fabrication of MEMS acoustic sensor. The MEMS acoustic sensors were fabricated by etching ZnO layer in three different etchants: HCl, NH4Cl with electrolytically added copper ions, and NH4OH with electrolytically added copper ions. For the first time, a technique is reported, which uses aqueous NH4OH solution with electrolytically added copper ions for etching of ZnO layer. For reliable operation of the device, the electrical testing of Al step coverage on ZnO layer was performed. The maximum currents that can be drawn across Al-deposited ZnO edge etched by HCl, Cu-added NH4Cl, and Cu-added NH4OH were 40 mA, 2.5 A, and 3.0 A respectively, without any damage to the structures. The investigations show that uniform Al step coverage on ZnO layer is obtained in case of NH4OH with electrolytically added copper ions. During fabrication of the device, a novel technique for building a microtunnel for pressure compensation was also developed. This microtunnel is used to compensate the pressure applied on the silicon diaphragm by connecting the cavity to the atmosphere. To realize the smooth inlet of microtunnel in the cavity, photoresist SU8 was used for patterning the cavity after microtunnel etching. The developed technique for microtunnel fabrication reduces the process complexity, providing improved yield of the device. The packaged device performed satisfactorily in the sound pressure level (SPL) of 120-160 dB over a wide frequency range of 30-8000 Hz. The maximum sensitivity of the sensor was measured as 380 μV/Pa.

Nanomaterials and Their Properties

The melange of definitions of nanomaterials is discussed. Terminology laid down by the International Organization for Standardization (ISO) and European Commission (EC) concerning nanomaterials is described. Ultrafine grained materials with grain size in nanoscale range show unusually higher mechanical strength than coarse-grained materials. Two vital characterizing parameters representing the degree of dominance of surface effects in materials are dispersion and coordination number. Due to predominance of surface effects, nanoparticles are efficient catalytic agents. Melting points of these particles are lower than those of the bulk material, and phase transitions are hazily defined. The onset of quantum size effect in nanomaterials depends on the dimension of the nanomaterial compared to exciton Bohr radius. Due to quantum confinement, the bandgap of a semiconductor nanocrystal is wider than that of the bulk semiconductor. Dependence of bandgap on nanocrystal size leads to emission of light of different wavelengths from these quantum dots. In metals, interaction of light with surface plasmons leads to resonance oscillations at particular frequencies, thereby producing different color effects. Notable magnetic properties of nanomaterials include the display of superparamagnetic behavior, the exhibition of magnetism in materials that are generally believed to be nonmagnetic, and the giant magnetoresistance effect.

Thick film, LTCC or silicon microhotplate for gas sensor and other applications

This paper presents the development of Pt heater using thick film, LTCC and silicon technologies. Miniaturized alumina hotplate can be used for sintering of metallized semiconductor devices and multiple gas sensor applications. For sensor application, thick film Pt heater was fabricated on back of the alumina substrate of size 5.0 mm x 5.0 mm x 0.6 mm by precise screen printing, drying and firing processes. The Au sensor electrodes were also printed, dried and fired in a similar way. Wire connections were made to the pads of Pt heater and sensor electrodes using parallel gap welder. Pt heater was operated up to about 600 degree celsius by applying electrical power. Wire connections of Ag alloy wire were found to be stable up to 700 degree celsius. For sensing LPG, smoke, this size of heater requires a power of about 2.5 W. Miniaturized alumina hot plate of size 12.5 mm x 12.5 mm x 0.6 mm has also been developed. Considering the low power requirement for modern sensors of the order of 0.5W or less, LTCC or Si based microhotplates are to be used. Silicon microhotplate has been developed at CEERI. Development work on microhotplate using LTCC has been started.

pH measurement of dirty water sources by ISFET: addressing practical problems

Purpose – To expose the gate of ion‐sensitive field‐effect transistor (ISFET) to filthy and muddy water, suspended algae, etc. investigate the influence of these conditions on device performance and suggest measures for using the device in applications where suspended soil particles are present.Design/methodology/approach – In this paper, cleaning procedure to make the blocked ISFET operative has been described. The effect of dirty water on pH sensitivity factor of ISFET, after it restarted functioning, has been measured. ISFET package has been modified. A relatively simple disposable nylon mesh with openings of size 100 μm for filtering bigger particles and lower for smaller particles, has been proposed for dirty applications to minimize device failures. This sieves away any dirt and thereby avoids failure.Findings – The device action is frequently blocked by deposition of dirt on the gate. Generally, it is recoverable by proper cleaning action although with reduced sensitivity. This necessitates recalib...

Simulation and characterization of dual-gate SOI MOSFET, on-chip fabricated with ISFET

The paper presents the process design, simulation and characterization of a silicon-on-insulator (SOI)-based dual-gate metal oxide field-effect transistor (DG MOSFET) with Al metal gate. The proposed structure is an N-channel device, using aluminum nitride (AlN) as gate dielectric. The fully depleted SOI-based DG ISFET compatible with the complementary metal-oxide-semiconductor (CMOS) process is considered to be a very promising bio-chemical sensor. Silvaco® TCAD tool is used to perform process design and simulations. The simulated and experimental results are compared, and are found to be in good agreement.