Anne J. Annema

Opto-electronic modeling of light emission from avalanche-mode silicon p+n junctions

This work presents the modeling of light emission from silicon based pþn junctions operating in avalanche breakdown. We revisit the photon emission process under the influence of relatively high electric fields in a reverse biased junction (>105 V/cm). The photon emission rate is described as a function of the electron temperature Te, which is computed from the spatial distribution of the electric field. The light emission spectra lie around the visible spectral range (k 300–850 nm), where the peak wavelength and the optical intensity are both doping level dependent. It is theoretically derived that a specific minimum geometrical width (170 nm) of the active region of avalanche is required, corresponding to a breakdown voltage of 5V, below which the rate of photon emission in the desired spectrum drops. The derived model is validated using experimental data obtained from ultra-shallow pþn junctions with low absorption through a nm-thin pþ region and surface coverage of solely 3 nm of pure boron. We observe a peak in the emission spectra near 580 nm and 650 nm for diodes with breakdown voltages 7V and 14 V, respectively, consistent with our model.

Monolithic optical link in silicon-on-insulator CMOS technology

This work presents a monolithic laterally-coupled wide-spectrum (350 nm < λ < 1270 nm) optical link in a silicon-on-insulator CMOS technology. The link consists of a silicon (Si) light-emitting diode (LED) as the optical source and a Si photodiode (PD) as the detector; both realized by vertical abrupt n+p junctions, separated by a shallow trench isolation composed of silicon dioxide. Medium trench isolation around the devices along with the buried oxide layer provides galvanic isolation. Optical coupling in both avalanche-mode and forward-mode operation of the LED are analyzed for various designs and bias conditions. From both DC and pulsed transient measurements, it is further shown that heating in the avalanche-mode LED leads to a slow thermal coupling to the PD with time constants in the ms range. An integrated heat sink in the same technology leads to a ∼ 6 times reduction in the change in PD junction temperature per unit electrical power dissipated in the avalanche-mode LED. The analysis paves way for wide-spectrum optical links integrated in smart power technologies.

An integrated optical link in 140 nm SOI technology

A silicon-on-insulator based optical link is introduced. Higher opto-coupling efficiency and temperature-resilience are obtained via avalanche-mode light-emitting diode operation against forward-mode operation. Self-heating induced thermo-coupling in steady-state is de-embedded by calibrating the photo-detectors photovoltaic characteristics.

A wideband IM3 cancellation technique for CMOS attenuators

In the receiver path and in spectrum analyzers, typically gain control blocks are used to limit the incident power to the level that the receiver circuitry can handle without degrading the linearity; in the transmitter path stringent power control is also desirable. Although variable-gain amplifiers (VGAs) traditionally implement the gain-control block, attenuators based on FET transistors show superior performances on linearity, power handling capability and power consumption.

On frequency-based interface circuits for capacitive MEMS accelerometers

Interface circuits for capacitive MEMS accelerometers are conventionally based on charge-based approaches. A promising alternative to these is provided by frequency-based readout techniques that have some unique advantages as well as a few challenges associated with them. This paper addresses these techniques and presents a derivation of the fundamental resolution limits that are imposed on them by phase noise. Starting with an overview of basic operating principles, associated properties and challenges, the discussions then focus on the fundamental trade-offs between noise, power dissipation and signal bandwidth (BW) for the LC-oscillator-based frequency readout and for the conventional charge-based switched-capacitor (SC) readout. Closed-form analytical formulas are derived to facilitate a fair comparison between the two approaches. Benchmarking results indicate that, with the same bandwidth requirement, charge-based readout circuits are more suitable when optimizing for noise performance, while there is still some room for frequency-based techniques when optimizing for power consumption, especially when flicker phase noise can be mitigated.

An Improved Analytical Model for Carrier Multiplication Near Breakdown in Diodes

The charge carrier contributions to impact ionization and avalanche multiplication are analyzed in detail. A closed-form analytical model is derived for the ionization current before the onset of breakdown induced by both injection current components. This model shows that the ratio of both injection current components affects the multiplication factor at relatively low fields before breakdown, but does not affect the reverse breakdown voltage. Furthermore, the model indicates that in case the ionization coefficients of electrons and holes are quite different in value, which depends upon the semiconductor material, the ionization coefficient of the charge carrier with the highest value can be extracted at those low fields. The one with the lowest value can be obtained by fitting the current close to breakdown. The model is compared and verified with TCAD simulations, and to some extent with experimental data, for silicon p-i-n diodes.

The Avalanche-Mode Superjunction LED

Avalanche-mode light-emitting diodes (AMLEDs) in silicon (Si) are potential light sources to enable monolithic optical links in standard CMOS technology, due to the large overlap of their electroluminescent (EL) spectra with the responsivity of Si photodiodes. These EL spectra depend on the reverse electric field. We present AMLEDs employing the superjunction (SJ) assisted reduced surface-field (RESURF) effect, which increases the uniformity of their electric field profile. Consequently, the EL area of these lateral devices is significantly enlarged as compared with conventional AMLEDs. Electrical and opticalmeasurements demonstrate RESURF, as predicted by TCAD simulations, and show a direct link between EL-intensity (optical power per unit device area) and the field profile. Contrary to a conventional AMLED, the breakdown voltage of the avalanche-mode SJ-LED scales with the device length. Furthermore, the brightest SJ-LED, with a lateral intensity of ~30 mW cm⁻² at an electrical power (<inline-formula> <tex-math notation=LaTeX>

Optical Power Efficiency Versus Breakdown Voltage of Avalanche-Mode Silicon LEDs in CMOS

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A 30fJ/comparison dynamic bias comparator

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Low power wide spectrum optical transmitter using avalanche mode LEDs in SOI CMOS technology

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