Abstract: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.

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 steadystate is de-embedded by calibrating the photo-detector's photovoltaic characteristics.

Abstract-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 electro-luminescent (EL) spectra with the responsivity of Si photo-diodes. These EL spectra depend on the reverse electric field. We present, for the first time, 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 to conventional AMLEDs. Electrical and optical measurements demonstrate RESURF, as predicted by TCAD simulations, and show a direct link between EL-intensity (optical power per unit device area) and the fieldprofile. Contrary to a conventional AMLED, the breakdown voltage of the SJ-LED scales with the device length. Further, the brightest SJ-LED, with a lateral intensity of ∼30 mW cm −2 at an electrical power (P AMLED ) of 0.1 W, shows a 2-fold higher internal quantum efficiency and a 3-fold higher EL-intensity compared to the conventional AMLED for the same P AMLED .

This paper presents a low power monolithically integrated optical transmitter with avalanche mode light emitting diodes in a 140 nm silicon-on-insulator CMOS technology. Avalanche mode LEDs in silicon exhibit wide-spectrum electroluminescence (400 nm < λ < 850 nm), which has a significant overlap with the responsivity of silicon photodiodes. This enables monolithic CMOS integration of optocouplers, for e.g. smart power applications requiring high data rate communication with a large galvanic isolation. To ensure a certain minimum number of photons per data pulse (or per bit), light emitting diode drivers must be robust against process, operating conditions and temperature variations of the light emitting diode. Combined with the avalanche mode light emitting diode's steep current-voltage curve at relatively high breakdown voltages, this conventionally results in high power consumption and significant heating. The presented transmitter circuit is intrinsically robust against these issues, thereby enabling low power operation.

For on-chip data communication with galvanic isolation, a monolithically integrated optocoupler is strongly desired. For this purpose, silicon (Si) avalanche mode LEDs (AMLEDs) offer a great potential. However such AMLEDs have a relatively low internal quantum efficiency (IQE) and high power consumption. For the first time, in this work, data communication in a monolithically integrated optocoupler is experimentally demonstrated. The novelty of this work is the use of highly sensitive single-photon avalanche diodes (SPADs) for photo-detection to compensate for the low IQE of AMLEDs. We investigated our optocoupler realized in a standard 140 nm CMOS SOI technology, without postprocessing, for various LED designs and points of operation. The power consumption of the AMLEDs is minimized through a novel AMLED design and employment of a low power LED driver circuit. The advantages of AMLEDs over forward biased Si LEDs are also demonstrated. For the best AMLED design, the achievable data rate is few Mbps and the energy consumption a few nJ/bit. The active area of the proposed systems is < 0.01 mm 2 .