Design and fabrication of a SiN-Si dual-layer
optical phased array chip
PENGFEI WANG,
1,2
GUANGZHEN LUO,
1,2
YANG XU,
3
YAJIE LI,
1,2
YANMEI SU,
1,2
JIANBIN MA,
1,2
RUITING WANG,
1,2
ZHENGXIA YANG,
1,2
XULIANG ZHOU,
1,2
YEJIN ZHANG,
1,2
AND JIAOQING PAN
1,2,
*
1
Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
2
Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
3
Beijing R&D Institute, VanJee Technology, Beijing 100193, China
*Corresponding author: jqpan@semi.ac.cn
Received 15 January 2020; revised 20 March 2020; accepted 2 April 2020; posted 2 April 2020 (Doc. ID 387376); published 26 May 2020
A SiN-Si dual-layer optical phased array (OPA) chip is designed and fabricated. It combines the low loss of SiN
with the excellent modulation performance of Si, which improves the performance of Si single-layer OPA. A novel
optical antenna and an improved phase modulation method are also proposed, and a two-dimensional scanning
range of 96° × 14° is achieved, which makes the OPA chip more practical.
© 2020 Chinese Laser Press
https://doi.org/10.1364/PRJ.387376
1. INTRODUCTION
With the development of autonomous driving, three-dimensional
imaging, remote sensing, and mapping, light detection and rang-
ing (LiDAR) has received great attention. Although there are vari-
ous LiDAR products on the market [1–5], they do not have
advantages in stability and price. These issues make these prod-
ucts unavailable, leading to the need to study new and better
LiDAR. The silicon-based optical phased array (OPA) is known
as the next generation product due to its low cost, fast speed, and
small size. More and more researchers have carried out research
on silicon-based OPA and achieved good results [6–21]. For
example, in the detection distance, the silicon-based OPA can
already detect a distance of 185 m, and the largest OPA has
1024 channels and is integrated with CMOS circuits. These
efforts have a very important impetus for the next generation
of LiDAR products.
However, silicon-based OPA also has many issues that need
to be solved, especially the loss of beam on the chip. Although
the processing technology of the silicon-optical platform is rel-
atively stable, there is still a loss of about 3 dB/cm for the optical
waveguide, and there are some additional losses, such as cou-
pling loss and transmitting and receiving loss. It is very unfav-
orable. Moreover, silicon has a strong nonlinear absorption
effect, such as two-photon absorption, free carrier absorption,
and large lowest order nonlinear effects, which makes the Si
single-layer OPA chip unable to handle higher energy light
[22]. The best results reported so far also have a total loss
of 5–10 dB, which mainly includes coupling loss, spectral loss,
and emission loss. If electro-optic phase modulation is used, it
will also introduce phase modulation loss, assessed according to
the on-chip loss of 10 dB. If the external APD is used to achieve
200 m of detection, an input power of more than 200 mW is
required. If the OPA chip is still used for detection, the input
power requires about 1 W of input power. This is obviously and
extremely disadvantageous for the application of long-range de-
tection. Compared with silicon, silicon nitride (SiN) has lower
loss. The thermo-optic coefficient of Si is five times that of SiN,
so the power consumption of the Si modulator is lower.
Therefore, if the low-loss characteristics of SiN and the good
modulation characteristics of Si are combined, it will be a very
good solution.
In this paper, we propose a SiN-Si dual-layer OPA chip,
which is fabricated on a SiN-on-SOI foundry platform. The
SiN is specifically Si
3
N
4
, and the refractive index at the wave-
length of 1550 nm is 1.996. The SiN layer is located above the
SOI substrate with a spacing of 150 nm silicon dioxide. The
silicon devices and the SiN devices are located on two layers and
do not interfere with each other. The front-end devices of the
OPA chip are some SiN devices, mainly including an input
coupler and a cascaded beam splitter, and each device is con-
nected through SiN waveguides. The back-end phase modula-
tors and optical antenna are both silicon devices and are
connected through silicon waveguides. The proposed SiN-Si
dual-layer OPA chip has excellent low-loss characteristics.
Because the front-end devices are made of SiN, the chip can
handle very large optical power, providing a basis for long-range
detection.
2. STRUCTURE AND CHARACTERISTICS
We have proposed a SiN-Si dual-layer OPA chip, as shown
in Fig. 1. The 220 nm top-Si SOI is the substrate, and
400 nm SiN is deposited on it by PECVD with a spacing
912
Vol. 8, No. 6 / June 2020 / Photonics Research
Research Article
2327-9125/20/060912-08 Journal © 2020 Chinese Laser Press