Nanoelectronics @ IIT Bombay


V. Ramgopal Rao and J. Vasi

Microelectronics has, for many years, been a major area of research at IIT Bombay.  In the year 2006, the Ministry of Communications & Information Technology launched a major initiative in the country to set up two Centres of Excellence in Nanoelectronics. IIT Bombay and IISc Bangalore, identified as having the two leading research groups in this area, were chosen as the sites for these centres.  These centres undertake state-of-the-art research in nanoelectronics, train manpower in this emerging area, interact with industry and research laboratories, and have created facilities which will be used by nanoelectronics researchers all over the country.  Though both the centres have some areas in common, by and large the team at IISc focuses more on the materials aspects of nanoelectronic devices, and the team at IITB focuses more on the devices and circuits aspects of nanoelectronics.  This is consistent with the expertise available at the two places, and the broad thrust of the two Institutes.  The total funding from the Government is Rs. 99.8 crores spread over 5 years, shared equally by the two Institutes.  Importantly, the two Centres were created via a single project, emphasizing the need for the two Centres to collaborate intensively with each other.

This major initiative from the Government has, during the past year, created tremendous interest from industry, as well as generated significant support from the Institute itself.  The Centre therefore represents a classic example of a successful government-industry-academia collaboration at a time when the semiconductor fabrication industry in India is ready to take off.

Much of the funding from the DIT project is targeted towards acquiring processing equipment aimed at creating a fully functional nanoelectronics laboratory.  Many equipments have already been installed and are in use.  One of the important pieces of equipment is an electron-beam lithography unit capable of writing 20 nm lines on a silicon wafer, with which nanoscale devices can be readily made.

The major industry supporter has been Applied Materials, Inc., the world’s leading semiconductor equipment manufacturer.  Applied Materials has endowed the “Applied Materials Nanomanufacturing Laboratory” by donating 3 major high-end semiconductor processing equipment valued at over $ 7.5 million.  These are the gate stack cluster tool capable of depositing the various layers (including high-k dielectrics) for a state-of-the-art CMOS structure, the PVD deposition cluster tool and the etch tool.  All of these are capable of handling 200 mm wafers.  Besides equipment donation, Applied Materials has sponsored several research projects, and has participated in a very successful student and faculty / engineer exchange program.  The Applied Materials Nanomanufacturing Laboratory was inaugurated in November 2007 by the President and CEO of Applied Materials, Mr. Mike Splinter, in an event which attracted significant local and global publicity. Besides Applied Materials, several other global industries, including Intel, Infineon, Renesas, and IBM are partnering with the nanoelectronics faculty for cutting edge research.

The Institute itself has generously provided funding, exceeding Rs. 12 crore, for the new Nanoelectronics building which is coming up, as well as for clean rooms, facilities, infrastructure, spares and maintenance.

The Centre for Excellence in Nanoelectronics at IIT Bombay has a major focus on multi-disciplinary research with a clear emphasis on product development meeting societal needs.  The centre facilities are currently being used by over 25 faculty members and their students from 9 different departments and schools at IIT Bombay. The centre is fast emerging as a hub for inter-departmental interactions at IIT Bombay. A few of the major research projects and initiatives currently underway at the IIT Bombay’s Centre for Excellence in Nanoelectronics involving faculty members from multiple departments and schools are summarized below.

A Point-of Care System for Cardiac Diagnostics:

According to some recent estimates, by 2010, over 60 % of the world’s cardiac patients will be in India. However, cardiac related care is almost non-existent in the smaller hospitals and primary healthcare centres, and this project is expected to fulfil this need. The idea is to develop low-cost diagnostic aids for cardiac dysfunctions. As part of this vision, there is an ongoing effort in the centre to develop an integrated system to provide point-of-care diagnostic support for cardiovascular diseases. The system under development monitors the molecular markers to detect cardiac attacks, especially the incipient cardiac attacks that go undetected before major/fatal attacks occur. The system comprises of “infarcSens” or “iSens”, which is a cantilever- and molecular FET-based affinity biosensor array for sensing myocardial infarction and subsequent cardiac status prognosis, using a suite of molecular markers. A low cost polymeric cantilever technology with embedded electrical readout schemes has been recently demonstrated in the group with electrical sensitivities in the range of a few ppm per nanometer of deflection, suitable for cardiac marker sensing. The sensing electronics is already in place while the associated data management software for tracking the markers with time, required for creating an epidemiological database, is currently being developed. A  multidisciplinary team consisting of Prof. V.Ramgopal Rao (EE), Prof. S.Mukherji (Bio-Dept), Prof. A.Q.Contractor (Chemistry), Prof. R.Lal, Prof. P.R.Apte, Prof. R.Pinto (all EE), and  Prof. Prasanna Gandhi (Mechanical Engg) and their students have been working on this project.

A Cantilever based Electronic Nose for Explosive Detection:

At IIT Bombay, in the Centre for Excellence in Nanoelectronics, explosive detection down to the parts-per-billion level of sensitivity for RDX and TNT has been demonstrated using an extremely sensitive and low cost piezo-resistive polymer cantilever structures. These detectors are meant for vapour phase detection of explosive molecules and come with an integrated wireless transmission capability. The surface stress which causes the deflection of the cantilever is generated from a selective chemical reaction on the surface of the cantilever. The cantilever surface can be regenerated after detection for subsequent measurements. The technologies are particularly suitable for wireless sensing networks and are extremely low cost. Further efforts are currently underway to improve on the selectivity aspect in order to make them useful for deployment in public places. The work is being carried out by Prof. V.Ramgopal Rao (EE), Prof. Soumyo Mukherji (Bio-Dept), Prof. Anilkumar (Chemistry), and Prof. Dinesh Sharma (EE) and his students.

Silicon Locket:

For mobile monitoring of ECG, a small toffee-sized low-cost locket has recently been developed in the centre by integrating a low power microcomputer with an indigenously developed operating system, analog front-end electronics and a re-chargeable battery with an in-built charger. The system is optimized to acquire a three lead simultaneous electrocardiogram (ECG), reconfigurable up to 12-leads, and can correct for motion artefacts arising out of the physical activity of the patient. The ECG data can be either stored in the Micro SD card memory, or transmitted through a phone modem or GPRS network. An arrhythmia event can be detected in real-time using the built-in algorithms and the system is configured to automatically inform a medical practitioner through SMS in the event of an arrhythmia. The system also allows the doctor to remotely login to the locket to view patient’s ECG in real time or download the data using a graphical user interface.  The locket is equipped with USB, IrDA and RS232 ports for seamless integration with public networks, mobile phones, and personal computers. An ultra low power custom made analog integrated circuit (IC) is designed and tested which performs all the data acquisition & signal conditioning. A low cost polymeric accelerometer technology developed in the centre is integrated into the electrodes to detect and remove motion artifacts in ambulatory subjects. A pluggable ultra-small PSTN modem is constructed to transfer data to a remote computer or medical database. A 32-bit system-on-chip based base-station is also developed as an accessory for the Silicon Locket. The base station is a handheld system with a higher processing power and a color TFT LCD panel. The base unit primarily has advanced in-built data management and analysis software for ECG analysis. The silicon locket, developed in cooperation with the Tata Consultancy Services, is the smallest wearable ECG recorder in the world, for its features. The technology is currently being transferred to an industry.  The contributors to this work have been Prof. D.K.Sharma, Prof. R.Lal, Dr. M.Shojaei (all EE), and Prof. S.Mukherji (Bio-Dept) and their students.

Disposable Organic Sensors with on-chip Electronics:

There is significant amount of activity in the centre for developing sensors using organic materials for a variety of applications, for sensing of biological reactions to physical measurands. A group of faculty members from the Chemistry Department (Prof. Anil Kumar, Prof. A.Q.Contractor), Bio-Dept (Prof. S.Mukherji) and EE Department (Prof. V.Ramgopal Rao), and their students are working closely in the Centre in synthesizing & engineering various organic molecules for specific sensing applications. Using solution processed organic materials, various organic circuits have also been recently demonstrated in the group. By integrating a high-k gate dielectric, low-voltage operation of these sensor circuits is demonstrated using solution processed organic materials. Currently a variety of projects are underway based on this approach.

Bottom-Up approaches for CMOS Scaling:

Porphyrin and metallo-porphyrin systems are excellent materials for molecular electronics, due to their diverse structural motifs and associated electrical, optical and chemical properties. The porphyrin SAMs engineered for specific applications are currently being explored in the centre as Cu diffusion barriers and for gate work-function engineering in CMOS. An inter-disciplinary team in the Nanoelectronics Centre has also been exploring the porphyrin SAMs for molecular electronics applications as well as for intercalation with DNA to realize a molecular switch with DNA acting as an interconnect. It has also been recently demonstrated that presence of aromatic rings in a porphyrin core would sterically hinder the Cu diffusion between molecules through the SAM layer, making it suitable as a barrier layer for Cu interconnects in ULSI CMOS technologies.  This work is being done by Prof. V.Ramgopal Rao, EE Department, Prof. M.Ravi Kanth and Prof. Anil Kumar, Chemistry and Prof. S.Mukherji, Bio-Dept and their students.

Future Generation Charge Trap Flash Memories:

The ever increasing demand for data storage is propelling a strong growth in NAND type Nonvolatile Flash memories. Unlike hard disk drives that store data on rotating magnetic disks, NAND Flash memories store data as electronic charges in memory transistors.  The scaling of NAND Flash to smaller cell sizes is a crucial aspect in meeting the high bit storage demand.  The currently used “floating-gate” memory cells are unlikely to respond to scaling, and are likely to be replaced by different types of cells.  One of these is the SONOS flash cell, and the other is the nanocrystal flash cell.   The Center for Excellence in Nanoelectronics, together with Applied Materials, USA, is engaged in materials innovation to tackle some of the issues observed in these types of cells.  Silicon Nitride (SiN), an insulator, is used as a charge storage element, and separated from the gate and substrate by oxide layers (hence the name SONOS).  Recently, the Centre and Applied Materials, in a project supported by Semiconductor Research Corporation (SRC), have created an engineered trap layer, i.e., a sandwiched structure consisting of two SiN layers having dissimilar composition (Si:N ratio) with a Silicon Oxynitride barrier layer. This new memory cell has shown much improved memory performance, and this ground-breaking work has recently received significant international publicity (seehttp://www.semiconductor.net/article/CA6562699.html).  Efforts are also underway to use semiconductor and metal Nano Crystals (NC’s) as the charge storage medium. In these memory cells, an insulating layer containing the nanocrystals (which trap charge) replaces the SiN layer in SONOS.  Though easy to fabricate, the finite density of states of semiconductor (silicon or germanium) NC’s limits the number of electrons that can be stored in semiconductor NC based storage (due to Quantum Confinement or QC effect) and hence the resultant memory window between high and low. Once again, IIT Bombay and Applied Materials are working together to develop both single and bi-layer metal NC based charge storage. Metal NC’s do not suffer from QC effect and offer extremely large memory window suitable for NAND applications. Efforts are underway to optimize the performance and reliability (cycling endurance) of metal NC systems.   The work on flash memories is being done by Prof. S. Mahapatra, Prof. J. Vasi (both EE) and Prof. G. Mukhopadhyay (Physics), and their students.

The facilities created in the Centres for Excellence in Nanoelectronics both at IIT Bombay and IISc Bangalore are being made available to students, researchers, scientists, and engineers from other organizations, including academia, industry and government through the ambitious separately-funded “Indian Nanoelectronics Users Program” (INUP).  The centres strongly encourage use of these facilities by all nanoelectronics researchers in the country.

In summary, the Centre for Excellence in Nanoelectronics at IIT Bombay (initiated as a joint project between IIT-B and IISc) is making rapid strides and making significant contributions to the society and the country in developing the much needed expertise in nanoelectronics in India.

For more information on the Centre for Excellence in Nanoelectronics at IIT Bombay, please visit: http://www.ee.iitb.ac.in/~nanoe.

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