Naga S. Korivi

Grayscale lithography by a polymer photomask doped with laser dye

This article reports on the development of a novel grayscale photomask which operates on the basis of differential absorption of ultraviolet (UV) light in photoabsorbing material. The developed photomask is made of a patterned, moldable polymer (polydimethylsiloxane) doped with a laser dye (Coumarin 314). The doped polymer functions as photoabsorbing material. Due to the moldable nature of polydimethylsiloxane, micro- and nanostructures can be created on its surface from a complementary mold relief. By adjusting the thickness of patterns formed on the photomask, concentration of the dye in the polymer, and UV exposure dose, a multitude of unique multidimensional microstructures can be fabricated with desired geometries and dimensions. Using the developed polymer photomask with a standard UV source, three-dimensional microstructures with different heights have been formed in positive photoresist by a single UV exposure step. This method is inexpensive compared to other grayscale lithography techniques and ...

A Generic Chip-to-World Fluidic Interconnect System for Microfluidic Devices

In the recent years, there has been considerable research interest in microfluidic devices which are based on the single or multiphase flow of liquids and gases through micro-scale channels or systems fabricated by micro-electromechanical systems (MEMS) technology. Due to their ability to perform complex, multiple tasks with biochemicals, such devices have many applications, especially in the biomedicine area and are expected to continue generating interest. However, due to the need for handling micro-scale flow of liquids and the diverse nature of microfluidic devices, some of the major challenges in their development are the establishment of chip-to-world fluidic interconnects and device packaging. This paper reports on the development of a generic fluidic interconnect methodology based on assembly and plugging-in of the components. This approach greatly simplifies the currently difficult task of implementing fluidic connections and provides an integration capability that facilitates the experimental development of microfluidic devices.

Texturing of silicon using a microporous polymer etch mask

This article reports on the texturing of silicon surface in microscale dimensions based on the formation of a polymeric layer on a silicon surface. The polymer layer is made porous by initially incorporating foreign material within it, followed by removal of the foreign material to leave behind pores. The pores in the polymer are of microscale dimensions having an interconnected structure, allowing the polymer layer to function as a chemical etch mask. The interconnected pores allow an etchant to access and etch the underlying silicon, resulting in texturing of the silicon surface. The texturing of silicon can be controlled, among other factors, by adjusting porosity in the polymer layer.

Built-in Current Sensor for High Speed Transient Current Testing in Analog CMOS Circuits

In this paper, we present a new built-in current sensor (BICS) for high speed, low voltage degradation transient current (IDDT) testing. This sensor has been designed using forward bias technique to limit the supply voltage degradation caused during transient current peaks to 2% of the supply voltage. A CMOS operational amplifier designed for operation at plusmn2.5 V in 0.5 mum n-well CMOS process is used as the circuit under test (CUT). The faults simulating possible short and bridging defects are introduced using the fault injection transistors (FIT). A total of twenty short faults have been introduced into the CUT and nineteen of them were detected, giving 95% fault coverage.

Built-in Current Sensor for Quiescent Current Testing in Analog CMOS Circuits

In this paper we present a new built in current sensor (BICS) for quiescent current testing- IDDQ. This sensor has been designed using forward bias technique to limit the supply voltage degradation caused by quiescent current passing through the BICS to 2% of the supply voltage. A CMOS operational amplifier designed for operation at plusmn 2.5 V in 0.5 mum n-well CMOS process is used as the circuit under test (CUT). The faults simulating possible short and bridging defects are introduced using the fault injection transistors (FIT). A total of twenty short faults have been introduced into the CUT and nineteen of them been detected giving 95% fault coverage.

A polymer microfluidic multiplexer

This paper reports on the development of a polymeric microfluidic multiplexer, which can be applied to perform a variety of functions involving liquid manipulation and control in microfluidics devices/systems, portable biosensors, and other miniaturized systems. The developed device was applied for 1times8 multiplexing of a test liquid, i.e., the test liquid was injected into the device through one inlet and injected out through eight similar outlets. It was also applied for the formation of micro-arrays of liquid drops on a surface. The device can be designed to deliver either a single or several different liquids.

Carbon nanotube nanocomposite-modified paper electrodes for supercapacitor applications

This paper describes the evaluation of carbon paper electrodes for supercapacitor applications. The electrodes are based on carbon micro-fiber paper modified with active material consisting of layers of silver nano-particulate ink and a nanocomposite of multi-walled carbon nanotubes and silver nano-particulate ink. The electrodes were characterized microscopically and electrically. Current–voltage studies revealed a consistent Ohmic behavior of the electrode when modified with different nanostructured active material. Among the active materials incorporated into the electrode, a nanocomposite of carbon nanotubes and silver nano-particulate ink significantly improved capacitance. The paper electrodes can be used for lightweight and ultrathin supercapacitors and other portable energy applications.

A Less Invasive Surgical Approach for Splanchnic Nerve Stimulation to Treat Obesity

Our group published a study in Obesity Surgery in 2009 on stimulation of the splanchnic nerve bilaterally in the abdomen of rats just above the celiac ganglion for the treatment of obesity [1]. This study demonstrated that food intake, fat to lean ratio, and metabolic rate were increased. Challenges included the invasive surgical approach and the problems with external wires. This letter describes a less invasive surgical approach, an implantable pacemaker, and the efficacy of unilateral splanchnic nerve stimulation. Prior attempts to stimulate the splanchnic nerve unilaterally for the treatment of obesity in humans have used a trans-thoracic approach with chest tube placement postoperatively [2]. Feeling that a surgical approach that did not enter the pleural or peritoneal cavity would be safer and less invasive, we performed a proof of concept study implanting a miniaturized programmable pulse generator into two Sprague Dawley rats using a posterior paraspinal approach described in detail by Celler and Schramm [3]. One rat was stimulated at 1.5 mA with 30 min off-time and 30 min on-time for 4 weeks, and the other implanted rat served as an un-stimulated control. Acute stimulation at 1.5 mA, despite being above the branch to the adrenal gland, did not increase blood glucose to suggest adrenal stimulation in rats. During the 4 weeks of stimulation while on a 60 % fat diet, food intake was reduced 5.4 % and body fat was reduced 0.5 % compared to the control. Body weight increased 5.4 % in the control while the stimulated rat lost 1 % of body weight (Fig. 1). The unilateral splanchnic nerve stimulation by a programmable implanted pulse generator implanted using a posterior paraspinal approach was well tolerated and effectively reduced food intake, body fat, and body weight.

Metal Patterning on Polymers for Flexible Microsystems and Large-area Electronics

Flexible microsystems and large-area, mechanically flexible electronic systems or macroelectronics, are attractive for a range of applications in consumer electronics, sensors, medical devices, and wearable microsystems. The techniques used for fabricating traditional microelectronic devices are not always applicable for macroelectronic devices. This paper investigates several approaches to precisely pattern metals and metallic thin films on flexible substrates. These approaches include photolithographic and non-photolithographic techniques. We have successfully accomplished precise patterning of metal thin Alms on flexible substrates made of polyimide (PI) and polyethyleneterephthalate (PET). Metals like aluminum, chromium, titanium and copper have been patterned on flexible substrates in this paper.

Sputtered germanium/silicon devices for photonics applications

We report on the ongoing investigation of magnetron sputtered germanium on silicon for photonics applications. Direct current (DC) magnetron sputtering has been used to deposit germanium layers on silicon at low growth temperatures and medium range vacuum levels. Standard photolithography has been used to make germanium photodetectors for the 1550 nm wavelength range. Electrical characterization, more specifically current-voltage measurements indicate that the devices function as intended. Sputtered silicon waveguides have also been fabricated and evaluated for possible applications in photonics integration. The sputtering-based developments in our present research are expected to provide for a flexible and economically viable manufacturing process for such devices.