A Test Vehicle for RF/​DC Evaluation and Destructive Testing Of Vertically Grown Nanostructures (VGCNS)

Research paper in the pro­ceed­ings of NT11 Inter­na­tion­al Con­fer­ence on the Sci­ence and Appli­ca­tion of Nan­otubes, Uni­ver­si­ty of Cam­bridge, Unit­ed King­dom, July 10–16, 2011.

We have devel­oped an RF test vehi­cle suit­able for mea­sur­ing DC and microwave per­for­mance of ver­ti­cal­ly grown car­bon nanos­truc­tures (VGCNS) as via-inter­con­nects. A first ver­sion of the inter­con­nect test vehi­cles devices were designed, fab­ri­cat­ed and char­ac­ter­ized. The RF small sig­nal (S‑parameter) and large sig­nal mea­sure­ments show that car­bon nanofi­bres can be used as inter­con­nects in microwave cir­cuit, even for pow­er devices. The design of test vehi­cle employs a three met­al lay­er con­cept, form­ing sequen­tial­ly the ground, sig­nal and device under test struc­tures for char­ac­ter­i­za­tion in a microstrip con­fig­u­ra­tion. The struc­tures as such con­sist­ed of inter­con­nects of dimen­sions rang­ing from 50 nm to 100 µm diam­e­ter made of VGCNS. In the first ver­sion of the inter­con­nect test vehi­cles, the inter­con­nects were made of car­bon nanofibers grown at 450 C. From SEM mea­sure­ment we found that the result­ing height was around 1.5–2 µm. Epoxy poly­mer SU‑8 was employed by spin­ning on the device and a sub­se­quent etch back process was car­ried out to open up the tip of the fibres to con­nect to con­sec­u­tive inter­con­nects with the third met­alli­sa­tion lay­er. After grow­ing the nanofi­bres, it was observed, using SEM, that inter­con­nect sizes small­er than 10 µm diam­e­ter suf­fered from par­a­sitic growth and there­fore the effec­tive device dimen­sion devi­at­ed from the ini­tial design. We car­ried out small sig­nal mea­sure­ments using a vec­tor net­work analyser for fre­quen­cy rang­ing from 1 to 25 GHz, in order to char­ac­terise the trans­mis­sion and reflection/​absorption of the devices as func­tion of their diam­e­ter size. The large sig­nal eval­u­a­tion was per­formed by mea­sur­ing the gain com­pres­sion of the devices. In addi­tion destruc­tive tests, aim­ing at test­ing the cur­rent car­ry­ing capa­bil­i­ty of the inter­con­nect, have also been per­formed. The resis­tiv­i­ty of inter­con­nects was mea­sured to vary varies from 0.2–1.3 mΩ·mm. Appar­ent­ly, the device per­for­mance is con­sid­er­ably influ­enced by the fill fac­tor of the inter­con­nect with VGCNS. Small vari­a­tions in fill fac­tor (in %) pro­vid­ed a large vari­a­tions in device resis­tiv­i­ty. Fur­ther­more, it was also observed that the resis­tance drops at high­er pow­er lev­els. RF con­duc­tiv­i­ty of inter­con­nects ranges from 5×103 S/​m to 7×105 S/​m. The aver­age input pow­er before inter­con­nect destruc­tion is larg­er than 25W with effec­tive device diam­e­ter rang­ing from 3 µm to 100 µm inter­con­nects. In addi­tion, the aver­age gain com­pres­sion before inter­con­nect destruc­tion was found to be 0.6 dB. It was not pos­si­ble to extract the con­duc­tiv­i­ty val­ue of an indi­vid­ual nanofiber using com­par­i­son to sim­u­la­tion data, since the devices might have suf­fered from par­a­sitic growth as well as pin­hole met­al dif­fu­sion dur­ing top met­al con­tact for­ma­tion. This cer­tain­ly affects the actu­al device dimen­sion and prop­er­ties. Nev­er­the­less, the proof of con­cept of design and man­u­fac­tur­ing a test vehi­cle for RF mea­sure­ments of ver­ti­cal­ly grown nanos­truc­tures was achieved. We will report the find­ings and anom­alies in the mea­sured devices. Fur­ther improve­ment is expect­ed in the com­ing test vehi­cle version.

Related insights from Smoltek

Hand held circular disc with Smoltek logo

Smoltek—from carbon nanofibers to mind-controlled robotic prostheses

Smoltek holds unique world patents for technologies that make material engineering on an atomic level possible. Smoltek has solutions that allow continued miniaturization and increased performance of semiconductors, contribute to carbon-free steel production and renewable energy storage, and enable mind control of robotic prostheses. This is a story of how Smoltek came to be.

License agreement for evaluation of CNF-MIM technology extended

Smoltek announces that the agreement signed with a global manufacturer of electronic components for technical and commercial evaluation of the company's CNF-MIM technology will be extended until the end of March 2021. In addition to further evaluation, the parties will also discuss the way forward after the evaluation, including a potential broadening of the collaboration.
Ola Tiverman, President Smoltek Semi

License agreement for evaluation of CNF-MIM technology extended

Smoltek announces that the agreement signed with a leading capacitor manufacturer for technical and commercial evaluation of the company’s CNF-MIM technology has been further extended, to December 31. At the same time, the parties have initiated a concrete dialogue on a possible continuation of the collaboration, with a decision to be expected during the first quarter of 2021.

Smoltek signs evaluation license agreement with leading passive components manufacturer

Smoltek announces that the company has signed yet another evaluation agreement, this time with a leading manufacturer of passive electronics components including capacitors. The agreement relates to an evaluation license where Smoltek's patented carbon nanofiber-based CNF-MIM technology is evaluated in a joint project. The order value for this first step amounts to approximately SEK 1 million and is intended to lead to a production license agreement in the next step.