Realizing 3D Smart Dust Particles Zeynep Dilli

11 April 2005 Introduction & Outline MIT Lincoln Laboratories FDSOI Process: Adapted to chip stacking 3D Run in April 2005 Outline:  System Description  Process information  Photodiodes: Design and Layout  Simulation Results  Layouts

11 April 2005 Proposed System 3D system concept: Three tiers  Sensor (Energy harvesting/Photosensor)  Storage (Energy)  Electronics (Local Oscillator and Output Driver)

11 April 2005 Proposed System Submitted proposal for a self-powered local oscillator circuit Area Assigned: 250 microns by 250 microns Total size: 250 x 250 x 800 microns ipip

11 April 2005 Process information 0.2 μm, fully depleted Silicon-on- insulator Silicon islands 50 nm thick Three-metal process Three tiers stacked Through-vias Top two tiers turned upside-down Figure adapted from MIT_LL 3D01 Run Application Notes

11 April 2005 Photodiodes: Design Issues Photocurrent=Responsivity [A/W] x Incident Power Responsivity= Quantum efficiency x λ [μm] /1.24  For red light, λ [μm] /1.24 = 0.51 Incident Power = Intensity [W/μm 2 ] x Area [μm 2 ]  Sunlight intensity ≈ 1x10 -9 W/ μm 2 Quantum Efficiency = [# electron-hole pairs]/ [# incident photons]  Depends on reflectance, how many carrier pairs make it to the outer circuit, and absorption  At 633 nm (red light), absorption coef. ≈3.5e-4 1/nm  amount of photons absorbed in 50 nm depth is (1-exp(- α d)) ≈  η = x reflectance x ratio of non-recombined pairs ≈ x 0.75=0.013  Photocurrent=0.013 x 0.51 x 1x10 -9 x Area [μm 2 ] = 6.63 pA/μm 2 Major problem: The material depth is very small

11 April 2005 Photodiodes: Design Issues  Photocurrent=0.013 x 0.51 x 1x10 -9 x Area [μm 2 ] = 6.63 pA/μm 2 Photosensitive area is pn-junction depletion region width (W d ) times length Available implants: Body threshold adjustment implants (p- type CBN and n-type CBP, both 5x10 17 cm -3 ); higher-doped source-drain implants and capacitor implants; undoped material is p-type, ~10 14 cm -3. Two diode designs: CBN/CBP diode and pin diode (CBP/intrinsic junction)  CBN/CBP diode Wd= μm; A= μm 2  Pin-diode Wd ≈ 1.5 μm; A=15 μm 2; possibly problematic  Layout: 2062 CBN/CBP diodes: 7.48 nA; 52 pin diodes: 5.17 nA To increase: Higher-intensity light; optimal wavelength (higher wavelength increases λ/1.24, but decreases absorption) Expect about 10 nA

11 April 2005 Photodiodes: CBN/CBP Diode Layout

11 April 2005 Photodiodes: pin diode layout

11 April 2005 Operation i p =10 nA, C=30 pF

11 April 2005 Operation i p =10 nA, C=30 pF

11 April 2005 Operation i p =10 nA, C=30 pF

11 April 2005 Operation i p =40 nA, C=30 pF

11 April 2005 Layout: Tier 1, Local Oscillator

11 April 2005 Layout: Tier 2, Capacitor Top plate: Poly Bottom plate: N-type capacitor implant, CAPN Extracted value: 29 pF Expected value: 30 pF

11 April 2005 Layout: Tier 3, Diodes and Pads “GND” “VDD” Oscillator output