Transistori ad effetto di campo con canale in grafene (GFET) aventi risposta fotoelettrica M. A. Giambra, E. Calandra, S. Stivala, A. Busacca DEIM Università di Palermo, via delle Scienze, Edifico 9, 90128, Palermo, Italia W. H. P. Pernice, R. Danneau Institute of Nanotechnology (INT), Karlsruhe Institute of Technology (KIT), 76344 Eggenstein Leopoldshafen, Germany Primo Workshop Nazionale "La Componentistica Nazionale per lo Spazio: Stato dell arte, Sviluppi e Prospettive" Roma 20/01/2016
Outline Introduction to graphene Graphene potentialities for space applications GFETs design GFETs fabrication Measurements DC RF/Microwave Optical Conclusions and future activities
flexible transparent wearable electronics, adaptable depending on exterior conditions, multifunctional can be tuned by application of electric fields, magnetic fields, pressure, and strain, green low power consuming, and ecologically friendly Why graphene? Graphene is paving the way towards a new era in the microelectronic industry. Potential impact in several fundamental areas: energy, defense, communications, electronics, artificial intelligence and information technology.
Graphene potentialities for space applications Graphene properties such as: superior mechanical and thermal stability, low power consumption, radiation hardness, make it ideal for space applications! Ultrasensitive chemical sensors for planetary science and heliophysics applications, strain sensors for structural health monitoring of spacecrafts photonic sensors for Earth science and heliophysics applications.
Graphene potentialities for space applications Graphene properties such as: superior mechanical and thermal stability, low power consumption, radiation hardness, make it ideal for space applications! Graphene Based Energy Storage Devices for Space Applications P. Mackey et al. Lunar Surface Applications Workshop, April 14 17, 2015 Graphene chemical sensors for heliophysics applications M. Sultana et al. Radiation Effects & Defects in Solids, 2013 Graphene Field Effect Transistors for Detection of Ionizing Radiation A. Patil, Nuclear Science Symposium Conference Record (NSS/MIC), 2010 IEEE
Introduction to graphene Graphene is a 2D crystal of carbon atoms arranged in a honeycomb lattice a = 2.46 Å AB = 1.42 Å B. Trauzettel, Physik Journal, 6, 39 (2007) High charge carrier mobility: 200.000 cm 2 V 1 s 1 (Si mobility: 1.000 cm 2 V 1 s 1 ) Mechanical strength: 1 Tpa Thermal conductivity > 3000 W/mK Optical absorption: 2.3% per layer Fullerenes (0D) Carbon nanotubes (1D) Graphene sheets (2D) A. K. Geim and K. S. Novoselov, Nature Mat., 6, 183 (2007)
Band structure and electronic properties of graphene Zero bandgap Valence and conduction band touch (K, K ) It presents a linear energy dispersion at low energies A. K. Geim and K. S. Novoselov, Nature Mat., 6, 183 (2007) A. K. Geim, Science, 324, 1530 (2009) Possibility to tune the Fermi level by applying an external electric field Modulation of interband transition Ambipolar field effect
GFETs design S S D G S S
GFETs Fabrication GFETs on insulating substrate (Sapphire) a) CVD grahene transfer and etching; b) Evaporation of Ti/Au Source and Drain via PVD; c) 10 nm Al2O3 dielectric via atomic layer deposition (ALD); d) Ti/Au top dual gate with different lenght patterned by e beam lithography; e) Deposition of Pd Pads via sputtering.
GFETs Fabrication
Measurements: Raman spectroscopy Noninvasive measurement; Measurements performed with: Renishaw spectrometer at 633nm, with notch filters cutting at 100cm 1 Incident power of 1mW Identifying graphenemonolayer: two most intense G peak at 1580 cm 1 and a band at 2700 cm 1 (2D). The G peak is due to the doubly degenerate zone center E 2g mode; 2D is the second order of zone boundary phonons; The peaks between 1250cm 1 and 1450cm 1 are the Raman spectrum of the sapphire substrate.
DC/RF Measurements Measurement Set up To VANA Source BB Bias Tee B Gate Drain Bias BBTee B Current meter Voltage source A V Voltage meter Source To VANA Voltage meter V A Current meter Voltage source
DC Measurements Gate sweep I ds (V gs ) Dirac point shifted: Hole/electron asymmetry Dirac point at positive gate voltages which means p doping Back sweep showed the hysteresis of the devices Hysteresis is caused by charge carriers trapped/detrapped at the impurities introduced by the gate dielectric or by interactions with water molecules attached to the substrate surface
DC Measurements Transconductance: g m I V ds gs
DC Measurements Drain Characteristics of built GFET: No saturation
De embedding process Electromagnetic simulations of the input and output launchers. The resulting scattering parameters were subtracted from the extrinsic structure in order to obtain the scattering parameters of the intrinsic structure (as in the scheme above).
EM simulations of launching structures E field (arrows) Current density (blue violet) NI AWR design Environment 3D EM Analyst
De embedding process Check of the de embedding (OPEN) It was possible to correct the raw data, by achieving a magnitude of the S 11 close to 1 and a phase shift close to 0, starting from a phase shift equal to 13 deg for the raw data for the check OPEN structure.
De embedding process Check of the de embedding (SHORT) ItwaspossibletoobtainaphaseoftheS11closeto180degandatthesametimeits magnitude close to 1, as expected from a SHORT structure.
RF Measurements Scattering parameters of one of the devices under study. De embedded measurements of input and output reflectances of OFF and ON devices are compared.
RF Measurements Raw data and de embedded measurements of the short circuit current gain and the MAG.
Comparison among different device geometries
Comparison among different device geometries f T Z OUT map: behavior of Z OUT as function of the geometric parameters Lg and : h21 map : behavior of the cut off frequency f T as function of geometric parameters Lg and. Notice that the behavior of the f T is not inversely proportional of the gate length L g
Optical Measurements f = 1.33 khz To VANA Source LASER ( = 405 nm) LASER DRIVER BB Bias Tee B Gate Drain Bias BBTee B f = 1.33 khz Current meter Voltage source A V Voltage meter Source To VANA Voltage meter V A Current meter Voltage source LOCK IN AMPLIFIER
Optical Measurements L g = 0.125 μm ; = 0.125 μm Photovoltaic effect Dependence on Vgs Linear trend with optical power
Optical Measurements L g =1.5 μm ; = 0. 5 μm
Conclusions and future activities Milestones Phase 1 Phase 2 Phase 3 GFETs design GFETs Fabrication Measurements Future activities New chip design and fabrication Development of a graphene mixer for optical frequency conversion Integration of graphene in optical waveguides