Maaike Op de Beeck

Nanoscaled interdigitated electrode arrays for biochemical sensors

Abstract Nanoscaled interdigitated electrode arrays were made with deep UV lithography. Electrode widths and spacings from 500 down to 250 nm were achieved on large active areas (0.5×1 mm). These electrodes allow for the detection of affinity binding of biomolecular structures (e.g. antigens, DNA) by impedimetric measurements. Such a sensor with Pd electrodes on SiO 2 is developed and theoretically analysed. It was experimentally characterised in KCl solutions demonstrating its bulk-insensitive behaviour and the immobilisation of glucose oxidase (GOD) could be monitored by measuring the double layer impedance.

Manufacturability issues with double patterning for 50-nm half-pitch single damascene applications using RELACS shrink and corresponding OPC

A double patterning (DP) process is discussed for 50nm half pitch interconnects, using a litho-etch-litho-etch approach on metal hard mask (MHM). Since an 0.85NA immersion scanner is used, the small pitch of 100nm is obtained by DP, the small trenches are made by a Quasar exposure followed by a shrink technique. The RELACS® process is used, realizing narrow trenches with larger DOF and less LER. For mask making, a design split is carried out, followed by adjustments of the basic design to make the patterns more litho-friendly. Assist features are placed next to isolated trenches to ensure sufficient DOF. Furthermore, an adjusted OPC calculation is carried out, taking into account proximity effects of both the exposure and the subsequent shrink process. After mask fabrication, this DP process is used for a single damascene application, with BDIIx as low-k material and TaN or TiN as MHM. Various problems are encountered, such as CD gain of the trenches during both MHM etch steps, poisoning and BARC thickness variations due to topography during the second litho step. For all these problems, solutions or work-arounds have been found, After the second MHM-etch, the 50nm half-pitch pattern is transferred successfully in the underlying low-k material.

Soft, Comfortable Polymer Dry Electrodes for High Quality ECG and EEG Recording

Conventional gel electrodes are widely used for biopotential measurements, despite important drawbacks such as skin irritation, long set-up time and uncomfortable removal. Recently introduced dry electrodes with rigid metal pins overcome most of these problems; however, their rigidity causes discomfort and pain. This paper presents dry electrodes offering high user comfort, since they are fabricated from EPDM rubber containing various additives for optimum conductivity, flexibility and ease of fabrication. The electrode impedance is measured on phantoms and human skin. After optimization of the polymer composition, the skin-electrode impedance is only ∼10 times larger than that of gel electrodes. Therefore, these electrodes are directly capable of recording strong biopotential signals such as ECG while for low-amplitude signals such as EEG, the electrodes need to be coupled with an active circuit. EEG recordings using active polymer electrodes connected to a clinical EEG system show very promising results: alpha waves can be clearly observed when subjects close their eyes, and correlation and coherence analyses reveal high similarity between dry and gel electrode signals. Moreover, all subjects reported that our polymer electrodes did not cause discomfort. Hence, the polymer-based dry electrodes are promising alternatives to either rigid dry electrodes or conventional gel electrodes.

Silicon Based System for Single-Nucleotide-Polymorphism Detection: Chip Fabrication and Thermal Characterization of Polymerase Chain Reaction Microchamber

A single nucleotide polymorphism (SNP) is a difference in the DNA sequence of one nucleotide only. We recently proposed a lab-on-a-chip (LoC) system which has the potentiality of fast, sensitive and highly specific SNP detection. Most of the chip components are silicon based and fabricated within a single process. In this paper, the newly developed fabrication method for the silicon chip is presented. The robust and reliable process allows etching structures on the same chip with very different aspect ratios. The characterization of a crucial component to the LoC SNP detector, the microreactor where DNA amplification is performed, is also detailed. Thanks to innovative design and fabrication methodologies, the microreactor has an excellent thermal isolation from the surrounding silicon substrate. This allows for highly localized temperature control. Furthermore, the microreactor is demonstrated to have rapid heating and cooling rates, allowing for rapid amplification of the target DNA fragments. Successful DNA amplification in the microreactor is demonstrated.

A Subcutaneous Biochip for Remote Monitoring of Human Metabolism: Packaging and Biocompatibility Assessment

This paper represents the extended version of the conference paper “Developing highly-integrated subcutaneous biochips for remote monitoring of human metabolism” presented at the IEEE Sensors Conference 2012, and presents data on assembly, packaging and short term in vitro and in vivo biocompatibility evaluation of a fully implantable biosensor array. The device was realized integrating three building blocks: 1) a multielectrode platform; 2) an inductive coil; and 3) an integrated circuit. The entire system measures 2.2 mm × 2.2 mm × 15 mm. Corrosion of electronic components and leaking of potentially hazardous substances in the body is prevented with a conformal coating of Parylene C, while an outer package of medical grade silicone was employed to create a soft shell suitable for implantation. Biocompatibility experiments did not show in vitro cytotoxicity in the considered period of 7 days, while comparison between 7 and 30 days in vivo implantations showed significant reduction of the inflammatory response in time, suggesting normal host recovery.

Vision: smart home control with head-mounted sensors for vision and brain activity

Today, an increasing number of household appliances is being connected to the Internet to form a smart home. Intelligent control algorithms in the cloud adapt the configuration of this Internet-of-Things to our daily routines and personal preferences. Frequently, there are unforeseen situations where the control algorithms will not capture the actual desired configuration. In these cases, the user must intervene in the control algorithms and manually adjust the connected objects setting. Browsing to the appropriate web service or launching the vendor-specific companion app for even a simple interaction like lowering the temperature setting is a tedious process. In this paper, we report on our early insights in building a mobile system that provides a common, intuitive interface to all actuators in the smart home. Using a head-mounted camera and a commercial Emotiv EEG neuro-headset, we let the user configure the IoT by merely looking at an object and performing a related facial expression. This way, users only need to look at an object and think about the desired action. We leverage on the home cloudlet for the compute-intensive signal processing for object detection.

Ultra-Thin Chip Package (UTCP) and stretchable circuit technologies for wearable ECG system

A comfortable, wearable wireless ECG monitoring system is proposed. The device is realized using the combination of two proprietary advanced technologies for electronic packaging and interconnection : the UTCP (Ultra-Thin Chip Package) technology and the SMI (Stretchable Mould Interconnect) technology for elastic and stretchable circuits. Introduction of these technologies results in small fully functional devices, exhibiting a significant increase in user comfort compared to devices fabricated with more conventional packaging and interconnection technologies.

Biocompatibility assessment of advanced wafer-level based chip encapsulation

Next generation implantable microsystem-based medical devices will have different packaging requirements than current implantable devices such as pace makers. While the packaging must remain biocompatible and provide a bi-directional diffusion barrier, it must also permit the biosensors, microelectrodes, etc to intimately interact with the extracellular environment. A CMOS compatible wafer level packaging strategy for die encapsulation has been developed and tested. TXRF measurements of 3T3 culture medium used in elution testing at physiological temperatures indicate the stack of PECVD diffusion barriers (SiC, SiN, SiO2) are effective in limiting Cu from leaching from the device. Additionally live-dead cell assays on in vitro co-cultures with both 3T3 fibroblasts and neonatal rat cardiomyocytes demonstrate the effectiveness of the different diffusion barrier stacks in preventing cytotoxic conditions.

A novel plasma-assisted shrink process to enlarge process windows of narrow trenches and contacts for 45-nm node applications and beyond

Limits to the lithography process window restrict the scaling of critical IC features such as holes (contact, via) and trenches (required for interconnects and double patterning applications). To overcome this problem, contacts or trenches can be oversized during the exposure, followed by the application of a shrink technique. In this work, a novel shrink process utilizing plasma-assisted polymer deposition is demonstrated: a polymer is deposited on the top and sidewalls of photoresist by alternating deposition and etch steps, reducing the dimension of the lithography pattern in a controlled way. Hence very small patterns can be defined with wide process latitudes. This approach is generic and has been applied to both contacts and trenches. The feasibility of the plasma-assisted shrink technique was evaluated through extensive SEM inspections after lithography, after shrink, and after etch, as well as through electrical evaluations.

Optical proximity effects and correction strategies for chemical-amplified DUV resists

Optical proximity effects (OPE) are narrowing the process window in the 0.25micrometers - 0.18micrometers CD range. Hence optical proximity correction (OPC) might be required. These proximity effects and correction strategies are studied in detail in this work. First, an evaluation methodology is derived for the three types of OPE (linewidth differences with pitch, end-of-line effects and corner rounding). Hence, the influence of various parameters on OPE is investigated for negative tone and positive tone resists, since clear differences exist in OPE for dark field and bright field masks. Linewidth differences with pitch are small for negative tone resists, end-of-line effects are less pronounced for positive tone materials. Obviously, optical parameters have an important influence on OPE. Also, loading effects during etch processes deserve attention. Aerial image based proximity correction is evaluated. With respect to CD variations with pitch, important improvements are obtained for some resists, but not for all materials. End-of-line effects and corner rounding are improved by the use of OPC in all our experiments. Superior proximity correction results are expected with the expansion of aerial image based OPC by implementation of resist models.