How to create a string in PHP that is equivalent to yyyyMMddHHmmssffff

I am trying to integrate with some VB code that generates a string using

DateTime.Now.ToString("yyyyMMddHHmmssffff")

The closest I can get to this in PHP has been

date('YmdHis')

But this lacks the milliseconds,

I have tried playing with microtime e.g.

date('YmdHis',time()).substr(str_replace(".","",microtime(true)),10,17)

But sometimes this results in a shorter string

>Solution :

date function always returns zero for microseconds. Use DateTime -> format and chop the last two digits off so that 4 fractional digits are left.

substr((new DateTime()) -> format('YmdHisu'), 0, 18);