Integrated Circuits

The workgroup circuit design is working on integrated circuit design. There are two main research areas, on the one hand analogue integrated circuits and on the other hand optoelectronic integrated circuits.

In the area of analogue integrated circuit design the integration of analogue circuits, e.g. operational amplifiers, mixers or filters, in state-of-the art nanometer CMOS technologies is the main focus. With the ongoing shrinking of the technology the supply voltages drop as well as the characteristics of the devices get worse and worse. These limiting conditions necessitate new concepts and innovative ideas in circuit design.

The second focus is on optoelectronic integrated circuits. The integration of photosensitive devices in CMOS and BiCMOS silicon technologies is the first step, the next one is the integration of complete optical receivers and signal processing.

Both research areas require beside careful design also the characterization of the realized microchips, which can be done in the own laboratory.

A variety of images of microchips to illustrate the work of the research unit. 4 opto receivers, 1 photo diode, 1 DC/DC converter, 1 wafer with probe needles of the wafer prober.

© Horst Zimmermann

Microchips of the research unit

Research Activities Overview

  • Optoelectronic Integrated Circuits (OEICs)
    • Integration of single photon avalanche detectors (SPAD)
    • Active quencher and gater circuits up to 9.9V SPAD excess bias
    • CMOS SPAD receivers
    • Bipolar SPAD receivers
    • Integration of avalanche photodiodes
    • Integration of photodiodes/phototransistors
    • Receivers for optical wireless communication (OWC) up to 3Gb/s and over 20m
    • Low noise optical receivers up to 11Gb/s
    • Low cost receivers
    • Optical distance measurement
    • Nonlinear optical receivers
  • Photonic-electronic Integration
    • 8×10Gb⁄s receiver
    • Modulator driver up to 10Gb⁄s
    • 4-PAM 10 GBd receiver and modulator driver
    • Low-power electronical control of 48×16 optical switch matrix
Wafer on the wafer prober with a picoprobe placed on the wafer for low-noise measurements.

© S.E.A.N.

Wafer prober

Research Capabilities

  • For design
    • Design framework: Cadence
    • Device simulation: advanced TCAD package for 2D and 3D simulations
  • For the characterization of photosensitive devices
    • On-Wafer, semiautomatic for serial measurements
    • Optical measurement sources in several wavelengths from infrared to blue
    • Probecard system for flexible contacting
Researcher uses the waferprober microscope under which a chip, probe needles and an optical fiber are placed.

© Horst Zimmermann

On-wafer measurement

For characterization of SPADs:

  • Completely darkened measurement setup (“dark-box”)
  • Fully automatic measurement of dark count rates, after pulsing probability and photon detection probability
  • Modulated laser source with very low optical power (few photons)
Picture: darkbox with xyz-stage for fiber positioning. Diagram: measurement results of quadruple SPAD sensitivity. Picture: quadruple SPAD receiver microchip

© Horst Zimmermann

Characterization of SPADs

For the characterization of optical receivers:

  • On-Wafer and connectorized
  • Bitpattern measurement test bench up to 10 Gb/s
  • Fast modulated laser sources (infrared to blue)
  • Fiber-bound and free space communication possible
Picture: Laser. Schematic: The complete circuit. Micro Photography: Optical receiver with satellite diodes for laser positioning.

© Horst Zimmermann

Characterization of OWC-receivers

  • For the characterization of optical distance measurement sensors:
    • Mechanical measuring bar, 3m
    • Fluxmeter
    • Optical powermeter
    • Mixed signal oscilloscope
  • Additional equipment:
    • Digital sampling oscilloscope (60GHz)
    • Single-shot oscilloscope (40GS/s)
    • Network and spectrum analyzer (3GHz + 20GHz)
    • Bitpattern generator (10Gb/s + 40Gb/s)
    • Bitpattern receiver (10Gb/s + 40Gb/s)
    • Multilevelgenerator
    • Attoamperemeter
    • Precision-LRC-meter
    • Optical Powermeter
    • Logic analyzer