Common anode addressable VCSEL

VCSEL (vertical cavity surface emitting laser) is widely used in various optical sensors due to its component characteristics, such as optical radar, facial recognition, gesture control, etc. In 3D sensing modules, addressable The VCSEL array can significantly reduce the area required for the die in the optical module, and the light output has high stability and can maintain consistent functions over a long period of time. However, as the driving conditions of IC components become faster and faster, the total Positive addressable VCSELarray are in demand.

In designing circuits, addressing vertical VCSEL designs usually makes circuit design simpler. All VCSEL components share a voltage cathode (anode), and the anode (cathode) of each VCSEL is connected to an individual control circuit. This

design can make the wiring of control signals simpler and reduce the complexity of the circuit. Why common anode? This is related to the choice of transistor in IC design. Taking BJT (MOS) as an example,there are two types of transistors: npn & pnp. However, npn has a much faster response speed than pnp because of electron migration. The influence of efficiency, how to match the two in the simplest way, the following circuit diagram is an example

pnp type BJT (MOS) + common cathode VCSEL
(b) npn type BJT (MOS) + common anode VCSEL
If the IC sensing module uses an npn transistor for higher speed driving, and the IC design pursues miniaturization, a controllable (addressable?) VCSEL array needs to be used. Only using a common anode VCSEL is able to reach the fast enough switching speed. This is Why common-anode addressable VCSEL array are in demand.

iReach is ready in the sensing field with two solutions in the common anode platform.

1. Wafer fusion Flip chip (common anode)

   iReach’s Cell products are manufactured through a wafer fusion process, where the native GaAs substrate is replaced with a transparent substrate. This addresses the light absorption issue associated with the GaAs substrate, ensuring a high-efficiency PCE . Furthermore, for Flip chip(Cell), there is less limitation of layout configuration to meet common-anode, common-cathode and even 100% individual emitter control.

   

2. Wafer fusion vertical chip(common anode)

   The most direct way to produce common anode chip is through epitaxial adjustment, such as using a P-type gallium arsenide substrate to grow a P/N switched reflective layer, or using a conversion layer to switch the VCSEL to npn polarity. However, the development of new epitaxy structure is very costed and time-wasting for verification. Considering the manufacturing, it also takes the longer product preparation cycle and much time for collecting the stability of production.
   iReach’s patented wafer fusion type flip-chip structure and the process, which allows the wafer to be flipped to a new substrate. It does not require additional development and verification time for epitaxy, and can be quickly introduced and re-fabricated to produce a stable, reliable and cost-effective common anode addressable VCSEL.The samples of both technology platforms can achieve photoelectric conversion efficiency (PCE) >50%(ex.3 junction).

   

At present, there are optical sensing modules for addressable VCSEL arrays on the market. The VCSEL part uses a traditional common cathode structure as an electrode to operate independently. However, as ToF's demand for high frequencies is getting higher and higher, IC design is being Challenges, as mentioned above, common anode addressable VCSEL is the answer. At present, there is no need to replace the original optical components. iReach quickly provides our design, allowing customers to quickly verify and adopt it into the original production line.

In many analysis reports, the use of VCSEL flip-chip has been seen in the iPhone 15 pro , just as what iReach always believe that flip-chip will be the future trend. VCSEL flip-chip can provide several advantaged for a ToF system. For example,there is no wiring process required for package, which not only eliminates the need for wire bonding, reduces the chip size without wire bonding pads, and, the most important, improves the capacitance and inductance effects induced by wire bonding, to make the signal switching speed faster.

For an ToF sensing module, the industry is looking for the solution which can miniaturize the optical parts, fulfill the requirement of nanosecond driving IC with common-anode design and addressable VCSEL arrays. iReach’s patented wafer-fusion VCSEL flip-chip, Cell, will be the most efficient, robust and reliable answer.