Semiconductor fabrication and characterization

Ultraviolet sensor design and fabrication

We design and fabricate ultraviolet photodetectors using silicon carbide. For detection of deep UV photons, Silicon Carbide (SiC) photodiodes have experimentally been shown to offer superior electrical and optical performance, surpassing detectivity of Photo Multiplier Tubes and silicon avalanche photodiodes (APDs). However, SiC, designs and fabrication techniques are not mature and at a relatively low technology readiness level, and the bulk of the SiC photodiode work has concentrated for near 300 nm photon detection where penetration depths are large. We work on a) establishing a processing methodology for high responsivity SiC APDs, b) increasing the detectivity of near 200nm photons that have very shallow penetration depths in SiC, and c) therefore increasing the technology readiness of SiC APD devices.


In addition to exhibiting large detectivity of deep UV photons, the large bandgap of SiC also provides the benefit of being blind to visible light, thereby obviating the need to utilize expensive, sometimes bulky and imperfect optical filters. SiC photon detectors also offer natural immunity to visible light leakage into the detector system. Thanks to its wide bandgap, SiC devices have the potential to provide more than fifteen orders of magnitude improvement in dark current background noise than their silicon analogues. These low dark currents, as well as further SiC material properties, also allow operation at elevated temperatures, favoring SiC photodiode use over their Si and PMT counterparts.

Long wave infrared sensor design and fabrication

We design and fabricate rectenna based systems to perform detection, communication, imaging and harvesting of high frequency electromagnetic radiation. Specifically, we design and fabricate rectenna based infrared sensors to detect 10 μm radiation.


The rectenna is a novel combination of a micro-antenna and a tunneling metal-insulator-metal (MIM) diode. This combination allows for conversion of electromagnetic radiation in the terahertz frequency range (AC) directly into direct current (DC).

Short wave infrared sensor design and fabrication

We are in the process of designing and soon fabricating SWIR sensors using germanium. SWIR range is a critical wavelength band for night vision applications as well as for special applications such as muzzle flash detection. Currently high performance SWIR sensors employ InGaAs detectors. It is our aim to design and fabricate Ge based SWIR sensors as alternatives to InGaAs detectors.

Other photodetectors

We have many years of experience on semiconductor device modeling (for example check citations below), and specifically on SiC devices and photon detector designs. As part of a previous work, we have helped researchers at NASA Goddard on modeling AlGaN UV photodetectors and accompanying SiC avalanche photodiodes for current multiplication. We have also designed drift detectors. As an example, a drift detector simulation showing calculated electric field profile is shown on the left. We have additionally worked on silicon photodetectors, designed as single photon avalanche photodiodes (SPADs). Related to our work on silicon photodetectors, we also show on the left calculations versus measurements for a silicon photodetector, indicating good match we had achieved between measurements and simulations. In summation, we have experience designing the following photodetectors in addition to those described above:
  • Heterojunction detectors.
  • X-ray detectors.
  • Silicon SPADs.
  • Drift detectors.

Semiconductor device electrical characterization

DC: Our electrical characterization setup includes various probe stations, parameter analyzers, as well as high, medium and low power source measurement units. We measure currents as low as 1 fA, and as high as 100 A. We also measure the breakdown characteristics of MOSFETs and diodes up to 5 kV.


AC: We take high and low frequency capacitance-voltage measurements up to 200 V.


Transient and RF: We use various custom circuits, as well as wave and RF generators to perform transient and RF tests.


Temperature (6K - 600K): We make current-voltage measurements down to 6 K using a cryostat, and up to 400 C using miniature heaters.


Partial list of test equipment employed:

  • Agilent B1500A Semiconductor Parameter Analyzer
  • Quadtech 7600 Plus LCR meter
  • Alessi Probe Station
  • Cryostat with 10K cold-head for cryogenic temperature testing
  • HP High Frequency Spectrum Analyzer
  • Tektronix High Frequency Scope
  • Agilent High Frequency Network Analyzer
  • HP Semiconductor Parameter Analyzer
  • Zeiss Stemi high magnification microscope ideal for examining integrated circuits
  • Collection of function generators, oscilloscopes, power supplies, etc.

Semiconductor device optical characterization

UV, Visible, SWIR: To carry out optical-electrical performance experiments, we use an instrumentation system comprised of a grating monochromator equipped with a broadband light source, a calibrated optical power meter, and various data acquisition hardware. To improve our electrical/optical testing capability, we purchase a laser driven wide range ultraviolet source, along with a monochromator for wavelength selection and bandwidth control. The laser has a relatively high flat optical power density in the 170 nm - 2 μm range, and is used for the assessment of our photodetector structures. In addition to the laser, we also have different gratings for our monochromator to achieve optimal control in the 170 nm - 400 nm range. We setup the laser and the monochromator, and also built a "dark" box for RF shielding and ambient light blocking. The system also includes a custom made nitrogen purging system. Additionally, we test packaged as well as unpackaged dies.


LWIR: Our measurement system uses a 30W air-cooled 10.6 μm laser. This is used in conjunction with various beam splitters, attenuators, and optical choppers. Additionally, the samples can be mounted on a movable stage with two servo motors. Furthermore, the system also includes complimentary peripherals such as lock-in amplifiers and low noise pre-amps.

Radiation testing and characterization

Total ionizing dose: We perform total ionizing dose radiation tests using gamma ray irradiations. These tests are performed at the University of Maryland (UMD) Co60 source at various dose rates. The irradiations are done in air, and special test fixtures are designed should there be a need to keep some of the devices at elevated temperatures during the total ionizing dose (TID) exposure. We also have necessary electrical testing equipment to characterize devices before, after and during irradiation. We previously performed TID testing on state-of-the-art CMOS devices and high power silicon carbide MOSFETs.


Rad Tests: In addition to TID testing, we can perform single event / heavy ion testing, and specifically neutron testing. We previously performed neutron testing of silicon carbide power devices (MOSFETs, diodes, bipolars) at the Los Alamos Neutron Science Center in New Mexico. Additionally we are involved in heavy ion failure modeling of power MOSFETs.

Nanofabrication

CoolCAD engineers have performed extensive nanofabrication work in materials processing, contact photolithography, anodic bonding, dry and wet subtractive processes, metal deposition utilizing resistive and e-beam evaporation, DC magnetron sputtering, electroplating, deposition of dielectrics utilizing RF magnetron sputtering and plasma-enhanced chemical vapor deposition (PECVD), as well as reactive ion etch rate optimization.


We also have experience using e-beam writers in conjunction with proximity correction algorithms to achieve feature sizes that are a few nanometers. This expertise is currently being utilized to fabricate rectenna structures, being used as infrared sensors. We also use e-beam metal deposition and various oxidation methods for the same process.

Application specific integrated circuit design and layout

A wide variety of ICs have been designed, fabricated and tested by CoolCAD personnel. More specifically, we have designed, laid out and tested ICs fabricated in the following technologies:
  • IBM 8RF
  • IBM 7HP
  • IBM 10LP
  • Jazz CA18
  • Peregrine 5FC
  • AMI/ON C5


We can design, layout and test ASICs in various technologies and at different complexities. We can also design and layout test chips for extreme temperature range SPICE model extraction for all n- and p-channel MOSFETs, and passives in a given process.

Wirebonding

We wirebond our own sensors and ICs. We can provide wirebonding services based on wedge or ball bonding techniques for low volume customers.

Related references

[Photodetectors]

M. Dandin, A. Akturk, B. Nouri, N. Goldsman, P. Abshire, "Characterization of single-photon avalanche diodes in a 0.5 micrometer standard cmos process. Part 1: perimeter breakdown suppression," IEEE Sensors Journal 10(11), 1682 – 1690 (2010).


M. Dandin, A. Akturk, A. Vert, S. Soloviev, P. Sandvik, S. Potbhare, N. Goldsman, P. Abshire, K. P. Cheung, "Optoelectronic characterization of 4H-SiC avalanche photodiodes operated in DC and in geiger mode," Proceedings of Int. Semiconductor Device Research Symposium (ISDRS), 1-2 (7-9 Dec. 2011).


A. K. Sood, R. A. Richwine, Y. R. Puri, A. Akturk, N. Goldsman, S. Potbhare, G. Fernandes, C.H. Hsu, J. H. Kim, J. Xu, N. K. Dhar, P. S. Wijewarnasuriya, B. I. Lineberry, "Design and development of carbon nanostructure-based microbolometers for IR imagers and sensors," Proc. of the SPIE 7679, 76791Q-76791Q-11 (2010).


A. Akturk, M. Dandin, N. Goldsman, P. Abshire, "Modeling of perimeter-gated silicon avalanche diodes fabricated in a standard single-well CMOS process," Proceedings of Int. Semiconductor Device Research Symposium (ISDRS), 1-2 (9-11 Dec. 2009).


A. Akturk, N. Goldsman, S. Aslam, J. Sigwarth, F. Herrero, "Numerical modeling and design of single photon counter 4h-sic avalanche photodiodes," Proceedings of Int. Conf. on Simulation of Semiconductor Processes and Devices (SISPAD), 201-204 (9-11 Sept. 2008).


[Radiation]

A. Akturk, J. M. McGarrity, S. Potbhare, N. Goldsman, "Radiation Effects in Commercial 1200 V 24 A Silicon Carbide Power MOSFETs ," IEEE Transactions on Nuclear Science 59(6), 3258-3264 (2012)


[Characterization]

S. Potbhare, N. Goldsman, G. Pennington, A. Akturk, A. Lelis, "Transient characterization of interface traps in 4H-SiC mosfets," Proceedings of Int. Conf. on Simulation of Semiconductor Processes and Devices (SISPAD), 177-180 (25-27 Sept. 2007).


A. Akturk, M. Holloway, S. Potbhare, D. Gundlach, B. Li, N. Goldsman, M. Peckerar, K. P. Cheung, "Compact and distributed modeling of cryogenic bulk mosfet operation ," IEEE Transactions on Electron Devices 57(6), 1334-1342 (2010).


[Nanofabrication]

N. Goldsman, F. Yesilkoy, S. Potbhare, M. Peckerar, A. Akturk, K. Choi, W. Churaman, N. Dhar, "Micro-Antenna Coupled Nano-MIM Diodes: Modeling, Design,Processing and Application," Proceedings of AVS 59th Int. Symposium & Exhibition, (28 Oct. – 2 Nov. 2012).


K. Choi, F. Yesilkoy, G. Ryu, S. H. Cho, N. Goldsman, M. Dagenais, and M. Peckerar. "A focused asymmetric metal-insulator-metal tunneling diode: Fabrication, dc characteristics and rf rectification analysis," IEEE Transactions on Electron Devices 58(10), 3519-3528 (2011).


K. Choi, F. Yesilkoy, A. Chryssis, M. Dagenais, and M. Peckerar. "New process development for planar-type cic tunneling diodes," IEEE Electron Device Letters 31(8), 809-811 (2010).

[ASICs]

Z. Dilli, A. Akturk, N. Goldsman, G. Metze, "Controlled on-chip heat transfer for directed heating and temperature reduction," Solid State Electronics 53(6), 590–598 (2009).