H.T.M. Pham

Bio: H.T.M. Pham is an academic researcher from Delft University of Technology. The author has contributed to research in topics: Silicon carbide & Surface micromachining. The author has an hindex of 10, co-authored 26 publications receiving 603 citations.

Comparison of porous silicon, porous polysilicon and porous silicon carbide as materials for humidity sensing applications

Abstract: This paper investigates the suitability of porous polysilicon and porous SiC as materials for sensing humidity. The investigation is a continuation of earlier work on porous single-crystalline silicon, where it was shown that this material was appropriate for humidity sensing, and could be easily integrated with standard Si processing. It was also shown that membrane structures enable the integration of a heating device to ‘reset’ the system. The best microstructure for humidity sensing was obtained for low-doped p-type silicon. The advantage of using polysilicon is that it is possible to tune its response (by doping) so that it has only a very small temperature coefficient of resistance. The idea is that a humidity sensor with a very small temperature dependence could be realised. The advantage of using SiC is that it offers the possibility of a humidity sensor that could withstand very harsh chemical environments.

Polyimide sacrificial layer and novel materials for post-processing surface micromachining

Abstract: We present a low-temperature post-processing module, utilizing polyimide as a sacrificial layer and novel materials such as PECVD SiC and metals (sputtered aluminium and titanium) as structural layers. The use of spin-on polyimide allows an all-dry final release step overcoming stiction problems often encountered in wet sacrificial etching processes. The spinning and curing procedure has been tailored to the specific needs of the IC-compatible post-process module. For the patterning of the polyimide, thin films of aluminium, PECVD silicon oxide or silicon carbide are employed as a mask layer. Anisotropic etching of the mask film and of the polyimide layer is accomplished by RIE. After patterning the structural layer, sacrificial etching of the polyimide is done using an isotropic dry etch process in high-density oxygen plasma. An underetch rate of 4 μm min−1 is achieved. Compatibility with different structural materials is tested and test structures are designed and realized in a fully post-processing surface micromachining module.

Fabrication of a CMOS compatible pressure sensor for harsh environments

Abstract: The fabrication and characteristics of CMOS compatible absolute pressure sensors for harsh environments are presented in this paper. The sensor which was fabricated using post-processing surface micromachining consists of 100 circular membranes with a total capacity of 14 pF. PECVD SiC was used due to its good mechanical properties, but since SiC has high resistivity, aluminium layers were used for electrodes. The stiction problems were avoided by using polyimide PI2610 as a sacrificial layer. The pressure sensors were fabricated and the change of capacitance over full pressure range, 5 bar, was 3.4 pF.

A porous SiC ammonia sensor

Abstract: When used as the dielectric in a capacitive sensing arrangement, porous SiC has been found to be extremely sensitive to the presence of ammonia (NH3) gas. The exact sensing method is still not clear, but NH3 levels as low as 0.5 ppm could be detected. We report the fabrication and preliminary characterisation of NH3 sensors based on porous SiC and Al electrodes. SiC is a very durable material and should be good for sensors in harsh environments. So far, the only NH3 sensors using SiC have been FET based, and the SiC was not porous. In our devices, SiC was deposited by PECVD on standard p-type single-crystal Si and was then made porous by electrochemical etching in 73% HF using anodisation current densities of 1–50 mA/cm2. Preliminary data is given for our devices response to NH3 in the range 0–10 ppm NH3 in dry N2 carrier gas.

Relative humidity sensors using porous SiC membranes and Al electrodes

Abstract: There is a need for humidity sensors that can operate in harsh chemical environments. In this respect SiC is a very promising material. Membrane humidity sensors using porous SiC as the (membrane) sensing element have been fabricated and tested. Earlier work established optimal anodisation conditions to make porous SiC (optimised for humidity sensing) to be: electrochemical etching in 73% HF, using an anodisation current density J A =1 mA / cm 2 . Due to the very low etch-rate of Al in 73% HF, we are able to use Al electrodes instead of Au, making the fabrication process of our sensors more cleanroom friendly. The response of porous SiC membrane devices, with sensitivities up to ∼200% will be discussed. Also, we will discuss the effects on sensor response of accelerated aging in an environmental test furnace and harsh environments such as the outlet of a car exhaust. SEM images are used to examine the membrane structures and porous SiC surfaces.

Phd by thesis

Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Metal oxides for solid-state gas sensors: What determines our choice?

Abstract: The analysis of various parameters of metal oxides and the search of criteria, which could be used during material selection for solid-state gas sensor applications, were the main objectives of this review. For these purposes the correlation between electro-physical (band gap, electroconductivity, type of conductivity, oxygen diffusion), thermodynamic, surface, electronic, structural properties, catalytic activity and gas-sensing characteristics of metal oxides designed for solid-state sensors was established. It has been discussed the role of metal oxide manufacturability, chemical activity, and parameter's stability in sensing material choice as well.

Humidity Sensors Principle, Mechanism, and Fabrication Technologies: A Comprehensive Review

Abstract: Humidity measurement is one of the most significant issues in various areas of applications such as instrumentation, automated systems, agriculture, climatology and GIS. Numerous sorts of humidity sensors fabricated and developed for industrial and laboratory applications are reviewed and presented in this article. The survey frequently concentrates on the RH sensors based upon their organic and inorganic functional materials, e.g., porous ceramics (semiconductors), polymers, ceramic/polymer and electrolytes, as well as conduction mechanism and fabrication technologies. A significant aim of this review is to provide a distinct categorization pursuant to state of the art humidity sensor types, principles of work, sensing substances, transduction mechanisms, and production technologies. Furthermore, performance characteristics of the different humidity sensors such as electrical and statistical data will be detailed and gives an added value to the report. By comparison of overall prospects of the sensors it was revealed that there are still drawbacks as to efficiency of sensing elements and conduction values. The flexibility offered by thick film and thin film processes either in the preparation of materials or in the choice of shape and size of the sensor structure provides advantages over other technologies. These ceramic sensors show faster response than other types.

Lab-on-chip technologies: making a microfluidic network and coupling it into a complete microsystem : a review

Abstract: Microfluidics is an emerging field that has given rise to a large number of scientific and technological developments over the last few years. This review reports on the use of various materials, such as silicon, glass and polymers, and their related technologies for the manufacturing of simple microchannels and complex systems. It also presents the main application fields concerned with the different technologies and the most significant results reported by academic and industrial teams. Finally, it demonstrates the advantage of developing approaches for associating polymer technologies for manufacturing of fluidic elements with integration of active or sensitive elements, particularly silicon devices.

Flexible Graphene-Based Wearable Gas and Chemical Sensors

Abstract: Wearable electronics is expected to be one of the most active research areas in the next decade; therefore, nanomaterials possessing high carrier mobility, optical transparency, mechanical robustness and flexibility, lightweight, and environmental stability will be in immense demand. Graphene is one of the nanomaterials that fulfill all these requirements, along with other inherently unique properties and convenience to fabricate into different morphological nanostructures, from atomically thin single layers to nanoribbons. Graphene-based materials have also been investigated in sensor technologies, from chemical sensing to detection of cancer biomarkers. The progress of graphene-based flexible gas and chemical sensors in terms of material preparation, sensor fabrication, and their performance are reviewed here. The article provides a brief introduction to graphene-based materials and their potential applications in flexible and stretchable wearable electronic devices. The role of graphene in fabricating ...