Postgresql如何存储PHP microtime（true）

I am trying to store PHP microtime to postgres DB, i tried to use timestamp datatype however i got an error.

this is how i am trying to store it to BD (Laravel framework)

<?php
    $transactionDbModel = \App\Db\PaymentTransaction::find($transaction->id());
                $transactionDbModel->payment_id = $payment->id();
                $transactionDbModel->type = $transaction->type();
                $transactionDbModel->amount = $transaction->amount()->value();
                $transactionDbModel->currency = $transaction->amount()->currency();
                $transactionDbModel->invoice_number = $transaction->invoiceNumber();
                $transactionDbModel->reference = (string) $transaction->reference();
                $transactionDbModel->status = $transaction->status();
                $transactionDbModel->psp_reference = $transaction->pspReference();
                $transactionDbModel->psp_status = $transaction->pspStatus();
                $transactionDbModel->microtime = microtime(true);
                $transactionDbModel->save();

Error:

Next exception 'Illuminate\Database\QueryException' with message 'SQLSTATE[22007]: Invalid datetime format: 7 ERROR: invalid input syntax for type timestamp: "1481195739.1502" (SQL: insert into "payment_transaction" ("id", "payment_id", "type", "amount", "currency", "invoice_number", "reference", "status", "psp_reference", "psp_status", "microtime", "updated_at", "created_at") values (a6094610-bd37-11e6-84f4-e710a59a6e32, a6072370-bd37-11e6-ab38-ad42705634e1, open, 175, GBP, , GQX3NITTRZ-20161208111538, done, 8824811960004172, Authorised, 1481195739.1502, 2016-12-08 11:15:39, 2016-12-08 11:15:39) returning "id")'

My question is what is the most suitable postgres datatype that can store php microtime(true)