Teaching integrated circuit and semiconductor device design in New Zealand: the University of Canterbury approach

Teaching the practical aspects of device and chip design in New Zealand presents many problems, including high manufacturing costs, long lead times, and the lack of local industry strength. Nonetheless, it is possible to overcome these issues. This paper describes the courses in these areas at the University of Canterbury, including a practical IC design project that has been running successfully for the past four years. The IC design project takes final year students through a full custom design using modern design tools and fabrication processes. The design is quite straightforward — a 4-bit arithmetic logic unit — but it emphasises the importance of design, simulation and testing. The final circuits contain a few hundred transistors, so good practice is essential. Twelve designs are integrated on to a single chip to keep costs down, and individual designs are addressed via multiplexers. The designs are fabricated using a 0.5 micron process, accessed through a multi-project vendor (MOSIS). Getting chips back from a manufacturer is significantly more motivating for the students than just performing a paper design

Surface texturing for silcon solar cells using reactive ion etching technique

Surface texturing is an effective and more lasting technique in reducing reflections and improving light trapping compared to antireflection coatings. A surface texturing technique using Reactive Ion Etching (RIE) method suitable for crystalline and multi crystalline solar cells, which resulted in surfaces with negligible reflection in the visible band is described. Different texturing structures (pillars, holes and black silicon) have been studied and compared in the wavelength range from 250nm-2500nm. It is found that the reflectance of the textured column structures were less than 0.4% at wavelengths from 500nm to 1000nm and showed a minimum of 0.29% at 1000 nm while the reflectivity from black silicon is around 1% and hole structures is around 6.8% in the same wavelength range

Control and measurement of hypoxia in microfluidic cancer assays

In this paper we will demonstrate spatially-resolved visualization of oxygen dissolved in a liquid medium and introduce two microfluidic devices for cell-culture experiments with integrated oxygen control. We will further show how these devices can be used to retain clusters or even individual cells within larger populations under hypoxic conditions, a capability which will allow the evaluation of cancer drugs on a cell-to-cell basis. In general, the combination of the oxygen sensor system with microfluidic culture devices has the potential to significantly improve the relevance of current cancer drug assays

Bioimprinted polymer platforms for cell culture using soft lithography

Background: It is becoming recognised that traditional methods of culture in vitro on flat substrates do not replicate physiological conditions well, and a number of studies have indicated that the physical environment is crucial to the directed functioning of cells in vivo. In this paper we report the development of a platform with cell-like features that is suitable for in vitro investigation of cell activity. Biological cells were imprinted in hard methacrylate copolymer using soft lithography. The cell structures were replicated at high nanometre scale resolution, as confirmed by atomic force microscopy. Optimisation of the methacrylate-based co-polymer mixture for transparency and biocompatibility was performed, and cytotoxicity and chemical stability of the cured polymer in cell culture conditions were evaluated. Cells of an endometrial adenocarcinoma cell line (Ishikawa) were cultured on bioimprinted substrates. Results: The cells exhibited differential attachment on the bioimprint substrate surface compared to those on areas of flat surface and preferentially followed the pattern of the original cell footprint. Conclusions: The results revealed for the first time that the cancer cells distinguished between behavioural cues from surfaces that had features reminiscent of themselves and that of flat areas. Therefore the imprinted platform will lend itself to detailed studies of relevant physical substrate environments on cell behaviour. The material is not degraded and its permanency allows reuse of the same substrate in multiple experimental runs. It is simple and does not require expensive or specialised equipment. In this work cancer cells were studied, and the growth behaviour of the tumour-derived cells was modified by alterations of the cells’ physical environment. Implications are also clear for studies in other crucial areas of health, such as wound healing and artificial tissues

The characteristics of Ishikawa endometrial cancer cells are modified by substrate topography with cell-like features and the polymer surface

Conventional in vitro culture studies on flat surfaces do not reproduce tissue environments, which have inherent topographical mechanical signals. To understand the impact of these mechanical signals better, we use a cell imprinting technique to replicate cell features onto hard polymer culture surfaces as an alternative platform for investigating biomechanical effects on cells; the high-resolution replication of cells offers the micro- and nanotopography experienced in typical cell–cell interactions. We call this platform a Bioimprint. Cells of an endometrial adenocarcinoma cell line, Ishikawa, were cultured on a bioimprinted substrate, in which Ishikawa cells were replicated on polymethacrylate (pMA) and polystyrene (pST), and compared to cells cultured on flat surfaces. Characteristics of cells, incorporating morphology and cell responses, including expression of adhesion-associated molecules and cell proliferation, were studied. In this project, we fabricated two different topographies for the cells to grow on: a negative imprint that creates cell-shaped hollows and a positive imprint that recreates the raised surface topography of a cell layer. We used two different substrate materials, pMA and pST. We observed that cells on imprinted substrates of both polymers, compared to cells on flat surfaces, exhibited higher expression of β1-integrin, focal adhesion kinase, and cytokeratin-18. Compared to cells on flat surfaces, cells were larger on imprinted pMA and more in number, whereas on pST-imprinted surfaces, cells were smaller and fewer than those on a flat pST surface. This method, which provided substrates in vitro with cell-like features, enabled the study of effects of topographies that are similar to those experienced by cells in vivo. The observations establish that such a physical environment has an effect on cancer cell behavior independent of the characteristics of the substrate. The results support the concept that the physical topography of a cell’s environment may modulate crucial oncological signaling pathways; this suggests the possibility of cancer therapies that target pathways associated with the response to mechanical stimuli

Fabrication of free-standing casein Devices with micro- and nanostructured regular and bioimprinted surface features

This work introduces a novel process for the fabrication of free-standing biodegradable casein devices with micro- and nanoscale regular and biomimetic surface features. Fabrication of intermediate polydimethylsiloxane (PDMS) moulds from photoresist masters and liquid-casting of casein is used to transfer arbitrary geometrical shapes onto the surface of casein devices. Casein film composition was optimized for mechanical stability and pattern resolution. It was found that 15% casein in 0.2% NaOH solution, mixed with 10% glycerol, and cross-linked by addition of 2% glutaraldehyde produced the best pattern transfer results. Biomimetic cell-like shapes were transferred onto casein by use of bioimprinting of two-dimensional cell-cultures into PDMS. To demonstrate this process, C2C12 mouse myoblasts were cultured on microscope slides, replicated into PDMS and casein using liquid casting and drying. Recessed alignment grids were integrated into the microscope glass slides to facilitate direct comparison of original cells and their bioimprints on PDMS and casein. Optical microscopy and atomic force microscopy confirmed the transfer of micron-scale morphological features, such as cell outlines, nuclei and larger lamellipodia, into the casein surface. Nanoscale feature resolution in casein was found to be limited compared to the PDMS intermediate moulds, which was attributed to limited wetting of the aqueous casein solution. Strategies to increase resolution of the casein transfer step, as well as degradation behavior of the fabricated devices in cell culture media are currently underway. Substrates fabricated with this process have applications in stem cell engineering, regenerative medicine, and implantable device

Microfluidic Devices for Cellular Bioimprint

We will discuss the advantages of using microfluidics for Bioimprint in general and of the two different platforms in particular. Both platforms allow for controls and experimental cultures to be carried out simultaneously. Similarly, time lapse samples can be taken from the same array minimizing variables between cell culture sets and thus enabling cell developmental studies

The fabrication of metallic nanotransistors

IEEE PressExtensive research studies have been devoted into the field of scaling down transistor size for ultra high density integrated circuits over the last three decades. It has been suggested that for the smallest possible scale of MOS transistor channel, a channel conductance close to that of a metal is required [1]. Metallic nanotransistors are based on field effect transistor made from metallic nanowires. This type of transistor operates by governing the flow of electrons through a narrow channel. In the fabrication of metallic nanotransistors, an electron beam lithography process has been developed to fabricate structures at the sub30nm scale using silver nanowires on SiN substrate. The single pass line exposure technique in electron beam lithography has been employed to define patterns of transistor structure as small as 20.2nm dimensions. This paper details the design and fabrication techniques of metallic nanotransistors. The limiting issues for writing sub30nm structures using EBL such as the charging effect of insulating materials, the proximity effects, and the single pass exposures are discussed