Browsing by Author "Arpiainen, Sanna"

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Advanced Diffusion Barriers for Copper Contacts on Silicon
(1999) Arpiainen, Sanna
Helsinki University of Technology | Master's thesis
IC-piirien metalloinnissa kuparilla (Cu) on perinteiseen alumiiniin verrattuna monia etuja, kuten alhaisempi resistiivisyys ja paremmat elektromigraatio ominaisuudet. Kuparia ei kuitenkaan voi laittaa suoraan kontaktiin piin (Si) kanssa, sillä se reagoi helposti muodostaen kuparisilisidiä, sekä diffundoituu piissä varsin nopeasti. Siksi Cu-Si rajapinnalla on käytettävä lisänä ohutta diffuusiovallia. Tässä työssä tutkittiin muutamien transitiometalleihin perustuvien diffuusiovallien kontaktiresistanssia vahvasti seostettuun n- ja p-tyypin piihin, sekä Cu/valli/Si kontaktirakenteiden metallurgista stabiiliutta lämpötilan (300, 400 ja 500 C) funktiona. Kontaktiresistanssin todettiin olevan riippumaton sekä vallimateriaalin työfunktiosta että kuumennuslämpötilasta, ja olevan kaikissa tapauksissa (n-Si) lähellä teoreettista arvoa arvioitaessa potentiaalivallin korkeudeksi kaksi kolmannesta kielletyn energiavyön leveydestä. Vaikka kontaktiresistanssi sinänsä ei riippunut kuumennuslämpötilasta, jo 300 C kuumennus paransi kuitenkin kontakteja poistaen niistä aiemmin havaittuja epälineaarisuuksia. Vallirakenteiden lämpötilakestävyys oli samankaltainen, tosin paikoin hieman huonompi kuin aiemmissa tutkimuksissa. Kuparin resistiivisyyden mittaus paljasti 30 nm paksun kromi (Cr) vallin pettäneen 400 C, ja tantaali (Ta) vallin 500 C kuumennuksen jälkeen, kirjallisuusarvojen ollessa 450 C ja 570 - 600 C. Kuparin resistiivisyydessä ei havaittu muutosta kuumennettaessa 30 nm titaani-wolframi, tai 10 nm titaani-nitridi ja titaani-wolframi-nitridi vallirakenteita viiteensataan asteeseen. Muutamia reaktiopisteitä oli tosin havaittavissa Ta näytteissä 400 C ja TiN näytteissä 500 C kuumennuksen jälkeen. Samalla metodilla tutkittiin myös Cu/valli/SiO_2/Si ja Cu/valli/SiN/Si rakenteiden kestävyyttä. Lisäksi havaittiin piin vahvan boori ja forforiseostuksen vaikuttavan kontaktirakenteen kestävyyteen. Työssä tutkittiin myös Deep Level Transient Spektroskopian (DLTS) käyttöä kuparin diffuusion toteamiseksi jo sen alkuvaiheessa kontaktin alle seostettujen n+p diodien avulla. Tämä ratkaisu osoittautui kuitenkin toimimattomaksi, sillä fosfori vaikuttaa kontaktirakenteen lämpötilakestävyyteen ja lisää kuparin liukoisuutta piihin niin, että diffundoitunut kupari ei läpäise seostettua kerrosta, eikä sitä siten voida havaita tyhjennysalueella. TiW ja TiWN osoittautuivat tässä tutkimuksessa parhaiksi diffuusiovalli materiaaleiksi. Erityisesti tulisi huomata, että TiWN valli oli vain 10 nm paksu.
Graphene Biosensor Programming with Genetically Engineered Fusion Protein Monolayers
(2016-03-30) Soikkeli, Miika; Kurppa, Katri; Kainlauri, Markku; Arpiainen, Sanna; Paananen, Arja; Gunnarsson, David; Joensuu, Jussi J.; Laaksonen, Päivi; Prunnila, Mika; Linder, Markus B.; Ahopelto, Jouni
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
We demonstrate a label-free biosensor concept based on specific receptor modules, which provide immobilization and selectivity to the desired analyte molecules, and on charge sensing with a graphene field effect transistor. The receptor modules are fusion proteins in which small hydrophobin proteins act as the anchor to immobilize the receptor moiety. The functionalization of the graphene sensor is a single-step process based on directed self-assembly of the receptor modules on a hydrophobic surface. The modules are produced separately in fungi or plants and purified before use. The modules form a dense and well-oriented monolayer on the graphene transistor channel and the receptor module monolayer can be removed, and a new module monolayer with a different selectivity can be assembled in situ. The receptor module monolayers survive drying, showing that the functionalized devices can be stored and have a reasonable shelf life. The sensor is tested with small charged peptides and large immunoglobulin molecules. The measured sensitivities are in the femtomolar range, and the response is relatively fast, of the order of one second. (Graph Presented).
Integration of 2D and 3D nanostructure fabrication with wafer-scale microelectronics: Photonic crystals and graphene
(2015) Arpiainen, Sanna
School of Science | Doctoral dissertation (article-based)
This Thesis considers different aspects of heterogeneous integration of 2- and 3-dimensional nanostructures with today's microelectronics process flow. The applications in the main focus are integrated 3D photonic crystals on a photonic chip and graphene biosensors, both exploiting directed self-assembly but at different length scales. View point is from the fabrication and integration challenges, but the future prospects of the selected fields of applications are also reviewed. Utilization of new materials and structures in microelectronics and photonics applications typically requires integration with the existing platforms. The fabrication processes are optimized for the established materials and generally require both high thermal budget and elemental purity to avoid contamination, thus the novel elements need to be integrated at the back-end phase and aligned with the pre-existing structures on the substrate. For that, there are basically three alternatives; (i) directed self-assembly, (ii) high precision placement and (iii) methods exploiting thin film growth and lithographic definition of the nanostructures. Whereas the 2D photonic crystals can be conveniently fabricated with advanced nanolithographic methods such as deep-UV lithography and etching, for the 3D photonic crystals the lithographic approach may not be the most efficient method. This Thesis presents a scalable directed self-assembly method for the fabrication of artificial opal photonic crystals on a photonic chip and defines the processing steps required for the inversion of the opal with silicon to obtain full photonic band gap without damaging the underlying chip. The existence of the full photonic band gap in the inverted silicon photonic crystal is demonstrated by measurements via the integrated waveguides. The integration of graphene with microelectronics processes is, in principle, simple due to the sheet-like structure of the material. The atomically thin 2D crystal can be processed in a manner similar to traditional thin films, as soon as graphene is on the substrate. This Thesis presents different methods aiming for scalable production of high quality graphene on different substrates, ranging from mechanical exfoliation based on step-and-stamp printing to rapid chemical vapour deposition with subsequent thin film transfer, which is the most promising method for large area graphene production. From the physical and chemical point of view, however, graphene is not a traditional thin film. Due to the single atom thickness, environment has a significant influence on the electronic properties of graphene. This has to be taken into account in the processing and design of graphene devices, but it also provides means to highly efficient sensing applications. The key issue in graphene based sensors is in the specific recognition, which has to be introduced by functionalization. This Thesis addresses the functionalization of graphene field-effect-transistors with self-assembled bio-receptors, utilizing non-covalent hydrophobic interactions between graphene and hydrophobin proteins.
Photoresponse of Graphene-Gated Graphene-GaSe Heterojunction Devices
(2018-08) Kim, Wonjae; Arpiainen, Sanna; Xue, Hui; Soikkeli, Miika; Qi, Mei; Sun, Zhipei; Lipsanen, Harri; Chaves, Ferney A.; Jimenez, David; Prunnila, Mika
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Because of their extraordinary physical properties, low-dimensional materials including graphene and gallium selenide (GaSe) are promising for future electronic and optoelectronic applications, particularly in transparent-flexible photodetectors. Currently, the photodetectors working at the near-infrared spectral range are highly indispensable in optical communications. However, the current photodetector architectures are typically complex, and it is normally difficult to control the architecture parameters. Here, we report graphene-GaSe heterojunction-based field-effect transistors with broadband photodetection from 730-1550 nm. Chemical-vapor-deposited graphene was employed as transparent gate and contact electrodes with tunable resistance, which enables effective photocurrent generation in the heterojunctions. The photoresponsivity was shown from 10 to 0.05 mA/W in the near-infrared region under the gate control. To understand behavior of the transistor, we analyzed the results via simulation performed using a model for the gate-tunable graphene-semiconductor heterojunction where possible Fermi level pinning effect is considered.